...and you have a 1/4" wrench, just stick the bit - alone - into the screw and use the 1/4" wrench (put it on the bit inside the trigger guard area) to turn it. It's a bit awkward, but it works.
I have a whole slew of allen-headed screws for both the trigger guard and the forearm. I bought 'em from Mcmaster, and had to get bags of 25. Send me your addy, and I'll send you the hardware along with the lock washers.