If you have other modelers around who have accumulated tanks over the years, ask them if they will let you try stuffing their extra tanks into your plane until you find one that works. Or, if you have a local hobby shop, take your plane down there and see what they can do for you.

Patching a tank is only delaying the inevitable, it's better to replace it.

Don

BTW: If the only reason you are saying you can find a replacement is because the hole shape in a bulkhead won't let you fit a different size/shape tank through it, there is no rule that says you can't cut/grind/sand the bulkhead hole larger to let another style/size/shape tank pass through it.