Ook. Over the years Arkham Horror/Eldritch Horror has accreted a legendarium part HPL, part other authors, part all its own. And given the example pages on the website, it looks like AH:tRPG uses a similar mechanic to the board games, as well as the same characters.
Though a) the Tékumel Foundation is doing a damn good job of keeping the original materials available and b) someone capable of giving EPT the OAR treatment would have to have good enough worldbuilding chops, I think, to do their own original property that, while blatantly inspired by Barker...
If I actually wanted it... I'd just wait a few years for backers to start dying and their estates being sold off. A few copies would likely hit Noble Knight.
One of the few times someone would have been better off going pro se, given the utter... somethingness of the counsel he did retain. (Better still not to have tugged into the Lone Ranger's wind in the first place, but some people gotta learn the hard way. If they even learn.)