I recently bought a classic Bridgestone Roadman with a stuck seatpost. I tried everything to remove the seatpost to no luck. So I dissolved the seatpost with sodium hydroxide and it worked magically.

Now my problem is that the seatpost I need is a 26.6 seatpost. I've tried going to several LBS and I couldn't find any. It seems like my last resort is to use my 25.4 seatpost and put a shim on it. Any ideas on how to make one? Thanks in advance.