If any WWII Airsoft weapon should be the "Holy Grail" this would be it. But, since the Thompson follows modern assault rifle form (pistol grip, long magazine under the receiver) and it was prominantly featured in a big Hollywood movie (Saving Private Ryan), Tokyo Marui took it upon themselves to create an almost perfect rendition of this this classic.
Every component that is metal on the real thing is metal on this one. The stock, pistol grip and foregrip are plastic, but you honestly can't tell until you touch them. Best of all, this beauty can be bought between $245 and $335, depending on the where you shop. Craft Apple Works makes a kit that will replace the plastic pieces with wood (about $180). In addition, Mousquito molds makes a very nice full metal conversion kit that turns the M1A1 into a M1928 (about $220). Really nice parkerized finish too. This kit replaces the entire upper receiver and barrel. Again, Craft Apple Works can supply a wood kit for rull M1928 realism. . This AEG takes a normal 8.4 volt large battery in the stock and produces about 270 fps. This is the one you want to buy if you're starting out in WWII Airsoft.
Where to Buy
You can pick this one up almost anywhere that sells airsoft guns. Overseas prices are about $215. Domestic prices are about $300. I suggest looking for a US based distributor. Stay away from Ebay and message boards. For a few dollars more, you will appreciate the security of ordering from a reputable vendor.
Other Information Sources
Some helpful sites and reviews of this weapon:
M1928 Conversion Kits (PDF of Den Trinity Site)