Well pictures would help, and pin diameter as well. Just off the top of my head, is there any way you can drill in from the opposite side and drive out the pin from there?
Any chance of getting a replacement lever? Thinking if you can find one and get the buggered one out, that may be a solution.
Lastly call/email Doug Turnbull Restorations and see what he suggests.
And is this your gun, or a customers gun? Yours, and if you're going to keep it, not a huge deal. If it's a customer's gun, ask him about it. Its an internal part so not likely to be visible from the outside.
ETA: Well after seeing the pics put while I was posting, I see drilling isn't an option as you would likely be coming from the top of the lever
Machine shop, your own drill press, or EDM if you can find someone.
After seeing the picture, I would most likely set the part in a vise and using successively larger drill bits, gradually drill out the pin. Let me know what you end up doing please. In case I run into this my self some day