That sucks, it seems parts availability is becoming more of an issue, I've always had super old cars and never really had trouble, but recently I've struggled with a few items. I think a lot of parts businesses got burned on obsolete inventory, so everyone is being a lot more conservative investing in old stuff now.
I'd be looking for a Ranger or S10/Sonoma, 4 cylinder models, as a suitable replacement. Those were so popular that parts availability is not an issue at all....for the GMs, LMC Truck has everything you could imagine in the way of restoration parts. There's probably someone similar for Fords too.