Yes, I know they are 5e, but it is a good list for conversions. I am going to contact the guy who signed up to convert them and see what he is doing.
As far as 3.5e conversions, I am going to keep looking and asking until I find them. I will not be giving up easily.
I suppose tenacity can be a virtue, but in this case I suspect you are headed for disappointment. Fifteen years ago, when the edition was new, there was a large and very active conversion community, converting pretty much everything that had been written for 1e/2e over to third edition, and people were excited to do things. But even at that community's height, all the H series conversions started with a flurry of excitement and for the most part never reached fruition. Nothing I saw suggested anyone ever finished a conversion document, and I found only one post that suggested anyone ever ran a successful H series campaign in 3e - and he said in the post he didn't want to share his material. I saw one prominent converter say he'd told his players that he'd convert the H series, but I don't know if anything came of that, and certainly there is not now a conversion document in the library.
When I converted I3, I spent about 60 hours on it. The resulting document was 64 pages long - exactly twice as large as the original document. It was also - despite containing none of the text of the original, no maps, and no basically no flavor text - pushing the boundary on what was legal because the strict interpretation of the rules regarding conversions put out by WotC allowed for no judgment calls, rebalancing, or otherwise making the module playable. Basically, they were wanting to protect their right to release official 3e 'Return to...' type modules, and as such did not want anyone to share work that would supplant that. And that's understandable, but it meant at the time that real conversions rather than just cut and paste out of the SRD work weren't strictly speaking sharable. I do know that it was used successfully by several EnWorlder's because they messaged me, but when EnWorld's database blew up my version of I3 disappeared and I never made an attempt to put it out there again.
My guess is that a true conversion of the H series runs over 200 pages of fairly small font in a Word document. I doubt one was ever finished. You might be able to find a conversion of H2, because that's by far the easiest to convert. But it converts to something like a rather awkward module for 13th-15th level characters. There are some notes for an attempted conversion of it already out there.
I guess what I'm trying (and failing) to say is two-fold.
First, your energy would be better spent converting it yourself. Even if you find what you are looking for, based on my experience with what most people put forward as 'conversion documents', it won't be all that useful to you anyway. It won't have the right amount of treasure for 3e's expected wealth by level. It won't offer the right amount of XP to follow the adventure path. It won't be balanced. It won't answer critical rules questions about skill use, or won't do it well. It won't offer the right sort of challenges to be interesting to a player of a 3e character. You'll find only the 'easy' things have been done, like copying stat blocks out of the SRD, which basically just saves you from flipping to the right page of the monster manual or cutting and pasting out of ENWorld's creature catalogue.
Secondly, if you really want to run an epic Orcus focused campaign in 3e, you'd be much better off finding a complete set of the Rappan Athuk books than trying to convert a set of modules that aren't that highly respected in the first place and which additionally poorly convert to 3e. If you want to borrow ideas from the H series for that adventure, then you certainly could, and it would be easier than trying to convert the H series wholesale.
