As wood becomes spalted (slowly rotting, though rotting might not be quite the best word in this instance), it gets softer and less strong/durable. The good news is that the spalting process often makes the wood very pretty. The strength left in the wood generally varies with the degree of spalting. My woodshop workbench is of spalted Ash (which I probably still have some of) and it's still concrete hard and would work fine for a pistol grip as is.
When I said that the spalted Pecan might need stabilizing, I meant that you don't want the wood to soften further and you'd like it to actually be a bit harder in order to tolerate use. It might be as simple as putting a few coats of Minwax water based Polyacrylic Varnish on it. That might work for your needs, though a pressurized resin would most certainly stabilize the wood. That's the pecan I'm talking about. You wouldn't need to do a thing to the spalted Ash. As for looks, the spalted Pecan is really pretty (mostly white, with black lines in it).
Drive up to see me and I'll give you a choice of Cherry, Walnut, Pecan, spalted Pecan, spalted Ash, Mesquite, and a few others. Probably nothing as fancy as you can get at Woodcraft, but it would be free. Free is good.