I forget if this is allowed or not but as they only appear once every few years and you asked:
Pentax RH B 70mm Lens Hood for Pentax 645 45mm F2 8 and 35mm 35 105mm F3 5 Zoom | eBay
I have been desperately searching for one for several years myself, but at that price its not worth it to me. I saved the picture of it though so I know about what I need to make it work on my FF film cameras.
Due to the way that original hood attaches with a tension fit and the fact that all the original rubber hoods are beginning to turn to plastic with age I have no idea how well it would work out.
If all you want is to use it on an APSC camera then just get the 3 position rubber collapsible ones, they vignette slightly at 35mm on FF in the corners but not at all on a crop sensor even fully extended which is surprising as its a super deep hood.
EDIT: sorry I missed the post where you said you already have one, dunno why it doesn't thread on, they are kinda cheap garbage so it could be the threads on the hood.
Do also remember that petal hoods don't work since its a rotating front element.
Last edited by PPPPPP42; 02-05-2014 at 10:12 PM.