Here's my take at answers. I hope others can provide more info.
1. I have not seen a conversion in person or advertised on Al Gore's invention, the internet. And if conversions are $400, I don't see why one wouldn't spend another $100 or so for an entire gun to have a spare frame. If Sig prices the conversions that high, I bet they don't sell many.
2. I'm quite happy with the accuracy with mine. I'm no crack shot by any means, but you can check out an off hand target of mine in the "Range Calls' thread in the "P250 Shooting" forum on this site. I suppose I'll bench it some day to see how accurate it really is. I will say that mine seems to shoot to point of aim with at least three different flavors of ammo.
3. I and others have reported light primer strikes with the gun. I think that issue is easily addressable (lighter firing pin spring, heavier hammer spring, shimmed hammer spring, lighter hammer, lighter firing pin, longer firing pin protrusion, etc are all possible remedies), so I'm not really worried about it. A guy on sigforums who apparently works at a gun range has a few 250s with thousands of rounds through them. He reported broken trigger bar springs after a large number of rounds. Again, this doesn't really worry me. Maybe Sig just needs a heavier spring or better quality control from suppliers.
4. Not to my knowledge, though I saw a 250 in forty in the gun case at my range just outside Austin, Tx.
