Old port versions?

Hi all, I've just now run into the situation where some code I'd like to compile (Cash, a scripting language, not available through macports) requires an older version of an installed package (ocaml, specifically it requires 3.09; 3.10 is current). It looks like it is normal to delete Portfiles for old versions of software (I don't see ocaml 3.09 anywhere). What is the reason for this? Sometimes the ability to install old versions of software is useful, and it seems like *extra* work to delete old Portfile versions. Is there a way for me to recover the ocaml 3.09 Portfile so I can install it alongside 3.10 (where alongside means, of course, only one is active at once). Thanks. -Denis