In the past they did, yes. It's been a while since I talked with them. Give them your specs and wants (slightly smaller dimensions are OK but not bigger, for example) and let them work on finding something that would work. I have no idea how much more it would cost to have it made to your custom specs, but it might be worthwhile to ask.
For what it's worth - I would be looking to go to plastic, as well, over aluminum.
You might check newer model Grady's, as well - for example, my mother has a 2000 model Tourney and it has a plastic tank. I think it's slightly bigger - but not sure exactly nor do I know if the dimensions would still work for you.
How much larger in each dimension (L, W, H) could you go and still have it fit? It would be good to measure that.
