If we're talking about OT graflexes, they were not HP boards. HP had some pretty distinctive patterns to their boards, and I'm 90% sure one was used for TFA.
The boards you want are probably industrial boards or computer extension cards. Thing is, we need straight leads (silver part), and at the time that was pretty rare. Industrial boards are large and have long leads that turn at right angles around chips and stuff. Extension cards are, literally, extenders so the leads go straight from socket to plug across the board. most others have swooping and curving leads that are usually too thick anyway, compared to the 22 or 44 pin gold plugs we want.
I used Otis elevator boards in my Skywalker Ranch saber, but again, only 1-2 boards have the right leads. I've also seen extension cards work too.
They also aren't guaranteed to be cheap. Some scrap places sell them for $20 or less, and some collector places sell the same boards for over $200. Considering the rarity of the boards themselves, in the prop community you see the correct ones sold for 60-100 bucks sometimes.
PM me if you'd like!