So my buddy has had his E1 g36c for a while and managed to loose the forgrip pin a year or so ago, and I just picked up a used JG g36 that was missing the front pin as well. Seeing as we are both poor and cheap and don't want to shell out $10+shipping for one replacement, I took a trip to home depot.
Unfortunately there were no steel rods in the right diameter, but I did find this:
As you can see I have cut it in two spots, and filed the ends down. Turns out it fits perfectly and is a cheap fix.
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Don't know if this helps anyone, but thought I'd post it just in case.