Have you got a price from your local Gehl dealer? you may be surprised how cheap they are.
I would guess they use the same basic taper locking setup that Bobcat uses, so your only real choice is to buy them genuine or machine your own and get them hardened. If they were a standard parallel type, you can get them from almost any where.
If you replace the pins, replace the bushings in the attach plate while your there, no point replacing a pin and not replacing the busing (if it has one).
Just my 2c worth.