Make your neck & pocket right in the first place, or build neck-through
Shouldn't be so difficult though, certainly nothing to justify those sorts of prices. If you know how much you want to shift the angle of your neck, then get the distance between your bolts, grab a calculator, apply a little basic trig and work out how much you need to adjust your neck by - you shouldn't need to shim the entire pocket unless you really seriously screwed up. Grab a set of calipers and a fine hand plane or card scraper, and take a thou or two off your neck as required.
If you think about it though - those shims are timber. Timber moves. This is why guitars have adjustable truss rods. Those shims
may have been relatively precise when they were made.. but they're not going to remain that way.