I do not have any sources of tin, but I suspect a web search would
turn up some.
I do want to make you aware that there are sources for a tin plating
solution that only requires that you dip the copper clad board in it
for a few minutes at room temperature.
http://www.vetco.net/catalog/product_info.php?products_id=936&gclid=CNPC5-rNq7wCFeZj7AodPA8ALgThere are other sources and a web search will turn up many. I have
used such solutions and they work quite well with no fuss.
Paul A.