Springfield makes the only production model 1911 9mm I know of. A friend of mine has one. It took some gunsmithing to get reliable feeding and it may take some magazine adjustment, but it is a good shooter. It has an integral ramp barrel so you would have to have a similar one, plus slide and internals to convert to .45
Colt made some with standard barrels. I have a 1991A1 and a .38 Super with 9mm barrel.
The STI Trojan 9mm gets good reports, but it is more expensive.
A .45 can be converted to 9mm with a whole upper, slide, barrel and all internals.
The change is not something you do at the range. The ejector must be changed out and it is held in by a small, tight pin. I have heard of leaving out the pin and just laying the ejector in its socket to be retained by the slide, but I don't know how well that would work.
Some say the frame feed ramps are different enough to make conversions impractical. Maybe so, but at one time Colt made a 9mm conversion kit themselves. I know of one .38 Super on a Gold Cup frame and a .45 on a .38 Super frame that work well. The 9mm is a little more trouble on the big 1911 but not too bad.