4-aminopyradine can be made in compounding pharmacies now. I've had it in my cupboard for years, though I heard that there was some trouble with it related to the fact that it has not been trialed in that form for the use in MS, but I'm not sure of the outcome of that. Here is an older reference about it http://www.mult-sclerosis.org/news/May2000/4APFAQ.html
My personal experience was less than great though it worked a little bit to improve heat tolerance and also let me go further and longer, but it also had the effect if making me feel spacey unreal or distant, if that makes sense, and also I tingled like CRAZY. I did not like it and took it only rarely when I felt the need for a boost (my daughter's wedding day for example).