Hey Jas,
Mate, look towards the bottom of the
forums listing page & you'll find the IIS classifieds. To be able to sell you need a minimum of 5 posts, which you've already gone over. To buy or reply to an ad you only need to join IIS.
You can still get yourself an OIII filter. While there is overlap between an OIII & UHC, there are differences that make having both good if you already have just an UHC.