I'm not aware of any mass produced rifle using a swamped barrel. It's more of a custom/semi-custom gun feature.
A custom gunmaker will build a gun specifically to your needs, but it will cost major bucks and you will wait a long time.
A semi-custom maker has certain "patterns" of guns that he makes with a list of available options. Many often have a few guns "on-hand" for sale. A semi-custom gun costs less, but will still be a chunk of money. A fairly plain rifle with a swamped barrel can be had for around $800-900. Another option is that many makers offer a gun "in-the-white" which means it is put together but requires final finishing of the wood and metal (final sanding/staining of the stock, blueing of the barrel) for a couple hundred less. Even cheaper is a kit, but requires some skill to put together.
The extra cost of a swamped barrel is because of the fair amount of extra work inletting it into the stock, but I feel the cost is well worth it.
Most of the semi-custom builders offer guns with straight octagon barrels for a couple hundred less than for a swamped barrel.
If you aren't looking to spend that much, a smoothbore would be cheaper.
The biggest advantage to buying a semi-custom gun is that you will get a QUALITY lock for the gun. I have no experience with the TC flintlocks, but many of the imported production guns have locks with unreliable ignition due to improperly hardened frizzens, bad springs, etc. A caplock of mediocre quality will usually function fairly well, a flintlock will not. If you're new to shooting flintlocks, you don't need to be handicapped with a bad one. Perhaps someone else can speak to how well the TC flintlocks work.
Here are some decent quality, reasonably priced semi-custom builders:
Tennessee Valley Manufacturing:
http://www.avsia.com/tvm/
Early Rustic Arms:
http://www.earlyrusticarms.com/main.htm
Jim Chambers Flintlocks (kits):
http://www.flintlocks.com/
PS: If you buy a mass produced flintlock, you can replace the standard lock with a good quaility lock made by L&R Lock Company. These are made to drop-in fit some production guns:
http://www.lr-rpl.com/ -look under the replacement lock section.