There are 3 extractors listed for the 5906, with 2 of them being revisions.
There are a couple of extractors listed for the 6906, with 1 being a revision.
Both models share one of the extractors.
Also, there are other 9mm extractors which can be used for repair in 9mm 3rd gen guns. One was the result of one of the Value Line guns having slide mass differences which affected "moment of mass" and general extractor functioning in that model. In at least 1 of the other repair extractors the hook is a couple thousandths of an inches shorter (and yet it still requires fitting). This wasn't discussed in any of the armorer classes, but was something I learned when discussing a problem with one of the repair techs one time. I've come across something similar before regarding an unusual difference in an extractor spring made for one production series of the 410, as I recall (because of a slide mass variation from other production runs).
The thing is that installing a 3rd gen extractor is not a "drop in" replacement procedure, especially when it comes to older 3rd gen guns (due to differences on machining and tolerances of the various parts). The older 5906's, for example, actually had 2 optional extractor springs, 1 of which used a 'nested' pair of springs. This was due to the older machining methods which involved more hand-operated equipment, and which could cause the depth and shape of the extractor spring hole to vary.
Fitting a S&W 3rd gen extractor requires a pair of tools, a bar gauge (Go/No-Go) to check the depth of the hook's reach, and a force dial gauge to check the tension of the spring (at a minimal deflection of the extractor tail). There's a standard recommended range of tension, although sometimes an older production gun might require a heavier tension in order to provide for proper functioning. There are heavier and lighter (than standard) extractor springs available to armorers in case a particular gun might require it.
The actual fitting of the extractor requires some careful filing on the adjustment pad of the extractor, located directly behind the hook. I've had some that required a lot of filing, and some that required only a couple of strokes. I've also encountered some variance when it came to having to use different extractor springs in order to get the tension within the recommended range ... and then had to carefully double check with live-fire to make sure the tolerance variations didn't introduce other issues (like feeding problems with a heavy spring). It can sometimes be harder with .40's because the heavier recoil of that cartridge could sometimes require an extractor in a particular gun be set so it blocked (with the bar gauge) very tightly.
Now, when I took my 4th armorer class for the 3rd gen guns a while ago, I learned that with the newest production guns and parts, every once in a while an extractor might indeed drop into a new production slide and actually fall within the expected tolerance without filing. The instructor told us that he'd seen it happen once recently during an armorer class. In the class I attended we had 2 extractors & 5906's fit together without having to be filed.
That's really unusual, and the best guess the instructor offered for it happening was that the latest of the continual & ongoing improvements in manufacturing were apparently resulting in much closer tolerances in some of the components (like the slides and the extractors, in this case).
If you need a new extractor installed in your 5906, I'd either have it done by the factory, or else by a gunsmith who is familiar with S&W 3rd gen guns and has the tools. (Unless you know a S&W trained armorer.)
FWIW, once a 3rd gen gun gets old & worn enough to start exhibiting chipping or breakage of the extractor hook, looking at both the extractor spring and the ejector is often a good idea. The ejector is the forgotten half of the hard working extractor/ejector team. It can get worn, too. It is a drop-in replacement, though.
Well, the only parts that require fitting nowadays on the 3rd gen guns are the extractor and the sear release lever.
Rarely a drawbar might require some filing to correct a Skip-DA issue (usually with a new drawbar being put in an older gun). It doesn't happen very often, though. I've only had to do it once out of more than a thousand guns I've helped support.
The barrels are coming much better machined and generally fit in newer production slides without fitting (filing on the barrel tab). (Tolerance is still checked with repair barrels, though, using appropriate feeler gauges.)
The use of the plastic disconnectors have eliminated the need for correcting (filing) for a "long-tail" disconnector condition. It's not even listed as a problem (or how to correct it) in the newer armorer manuals.
The ejectors have benefited from revisions and refinement over the years, too. The newer ones have longer tips for faster and more positive ejection, and the previous sharp corner/angle under the tip (to the rear) was eliminated, replaced with a curve, to help eliminate the potential for a stress riser to occur.
I'm not an expert on this, being just an armorer, but bottom line? This isn't a do-it-yourself kitchen table (or garage workbench) repair without some tools and knowledge.
Okay, I've rambled enough. Sorry.
Why not call S&W?