Try here, cut the url down to get to the home page...

Try here, if it not come to the product listing, use "DSP-74910A" as the keyword, and J&L as the vendor.

Here is another, Part Number 26005A214, little more expensive than the other 2....

Forgot here



Don't limit yourself to gunsmith supply, all this stuff is common machine tool stuff, though "special thread", so you might just get lucky and have a machine tool supply where you live that might have it on the shelf, or be willing to get it for you.