Here is a source of needle-bearinged 500 cranks for about $550 USD delivered, and a link to a 535 slightly higher CR piston.
I dunno where you'd get a crank repaired for that even if you supplied all the parts. This Price crank is about 1/2 of an H's crank but uses the stock pot metal rod. Not a real issue if you aren't going to buzz it.
Sounds like you are chasing the HP Demon. I'm ambivalent on changing cams. The stock bump sticks make good power appropriate for the design. Spinning up a Bullet sans a steel rod & well balanced crank, alloy barrel & tough forged piston is a dead end. A new stock-stroke crank and larger slug will liven things up a bit, but still requires a "mechanically sympathetic" rider. As you point out, there are savagely better designs on the market using Post-1940 engineering if you want to go fast. I'm constantly amazed at what $2500 will purchase, and how much performance is available for that meager amount.
The Price crank, piston and fitted alloy barrel will set you back about $1000 out of pocket. If you don't want to tear into it, maybe now's a good time to sell it to a fellow enthusiast and move on. Time is limited for all of us - if you'd rather be riding than wrenching, there's a LOT of available options, cheap.
https://www.pricepartmotorcycles.co.uk/ourshop/prod_2986111-144693sx-needle-crankshaft-500cc.html144693s/x needle crankshaft 500cc ; £375.00
Special crankshaft remanufactured for 500cc Bullet
New style needle bearing with 35mm diameter pin fitted.
Connecting rod has new bearing bush fitted and honed to use the 35mm needle bearing
This is on service exchange basis with a cost of £375.00
There is a surcharge of £50.00 if the returned crankshaft assembly is beyond repair, or the main drive or timing side shafts are damaged/worn
https://www.pricepartmotorcycles.co.uk/ourshop/prod_1090642-144162-87mm-high-compression-piston.html144162 87mm high compression piston ; £105.00
High Compression Piston 87.00mm standard size for Royal Enfield Bullet 535cc
Comes complete with piston rings, piston pin & retaining clips
Convert your 500cc to 535cc for that bit of extra power.
Please note, changes to carburation & timing may be required,
Warranty is restricted to faulty materials or product,
No other warranty can be given due to any fitting outside of our control
https://the-enfield-strikes-back.blogspot.com/