The forend screw is a standard thread size (1/4-20 or maybe 1/4-24) You may find a knob in a hardware store droor if you keep your eye's peeled.
You may also find a survivor forend on the classifieds here, if you'd like one. As for 'gunsmith fitting' well....you don't need a degree in rocket engineering to do it yourslef. (the degree is an option, but not really a requirement
) You put it on your gun. If it fits, you're done. If it's too tight, sand a little off. Too loose, acraglass or other filler and then sand it back. A little loose isn't a problem as long as the front doesn't fall off when you open the action, which would be a rare case indeed.
I'd look at either finding a knob, or just stick with the pocket screwdriver. Me, I have a Survivor and a couple of ther Handis. That's not the cheap way to go, but it's the way many on this board seem to have gone. Multiple rifles= all the options.