Olin,
Any remaining 2 ft. ga. engines in Mexico are on display, which means you will run into the Mexican cultural heritage and artifacts laws. Many have tried to repatriate steam from Mexico and all have failed, except for the Cripple Creek 0-4-4-0. How they got that out, I would be very interested in hearing. Look at all the time and trouble it took just to bring two PA hulks back to the US.
Brazil has a batch of very tasty 2 ft. ga. Baldwins and a couple of MLW's, rusting away at the Perus Cement Plant. There was a 4-6-0, a batch of 2-6-2's, a couple of 2-4-2's and the frames of at least two 2-6-0's and an 0-6-2 out behind the shops. 20 engines or parts of engines total. Most of them were still there last year when a friend visited.
Many have tried to buy these and failed, but they are the only engines that I know of that would be reasonably authentic for a Maine 2 ft. operation. Get some serious backing and go for it. You won't get them on the cheap, you will have to through official channels that will try your patience and your wallets, but where else can you find what looks like a Sandy River 2-6-0 or 2-6-2? For photos, find a copy of Roy Christians "World of South American Steam."
Someone mentioned Java. Both Java and India have 2 ft. ga. sugar mill lines and both countries have been willing to sell and export steam. Quite a few have gone back to the UK. I think there may be at least one or two Baldwins left in India. Some of the WW 1 4-6-0 and 2-6-2 trench engines may have gone to india. All the engines in Java are German or Dutch, but they are small and cute! You can get these home for a fair price.
If you wanted to try something completely different, South Africa still has 2 ft. ga. engines that can be purchased and exported, both 2-8-2's and 2-6-2+2-6-2 Garratts. Several have gone to the UK and Switzerland, as well as one each to Texas. Boilers can be built in the US. Any chance a 2-6-2 Garratt engine unit could be rebuilt into a prarie? You could probably buy a scrapper in South Africa for peanuts. Heck, you can buy a Northern for $20,000! Wrong gauge of course!
Good luck.