Rob, the Tamron SP 90mm f2.5 Macro lens is still made although now as a fixed mount Autofocus lens, available in a few mounts.
Two of my friends use one for their nature and wildlife photography, originally with a Pentax K mount adapter. The there was an extension tube available as well for 1:2 to 1:1 use.
I think the SP series were all Adaptall-II lenses, as long as you get this type it doesn't matter what mount is fitted as you can switch it to a Canon FD Apdaptall mount. I have a spare Canon FD Adaptall-II mount that I was sent in error, if you needed it you could have it for the cost of postage.
Ian