Sadly Parsimonious does not have it's own search engine and typically the things people ask for are files which are no longer on the site (so a search engine wouldn't do much good even if we did have one).
During 2008-2011 a large quantity of items were removed (in preparation for an updated version of the website). These are generally very old files which fall below the current quality standards of the site. These files have been re-homed, however and you should be able to find most (if not all) at:
Ginnie and her crew have worked tirelessly to rescue a huge quantity of content from sites like ours that like to have the occasional clear-out, and also sites which have closed their doors. You will need a Yahoo account to use the groups, additionally you'll need to ask the moderators where to find the files you're looking for, since they have many hundreds of groups for all the different sites they now host.
I'm sorry to say that I don't have a complete directory listing available - nor the time to put together a catalog to show pictures of these removed items so unless you are looking for a specific item there isn't really a general browsing option for this content, however as it was all removed for quality control reasons, you're really not missing out on any amazing gems!
In 2012 our Sims 1 Fashion section has been split into 2 sections, heads and clothing, meaning you'll find heads in their own separate category on the Sims 1 main menu.
The selection available are all completely new items made in 2011 onwards, all the old heads are available at Saving The Sims.