I had the same problem in the UK but managed to find two guys in the US that would supply a reconditioned crank at a reasonable price. I can only give you their contact info, as I found another used engine in the end to strip the crank out of, so didn’t need to buy from them. The quote below I received from Gavin.
1990 Supra Turbo 7MGTE engine parts:
TCK7M (Crankshaft with all bearings): US$270.00
2. TCR7M (Connecting Rod): US$38.00 per rod. US$228.00 for 6 connecting rods.
3. TOP7MS: (Oil Pump): US$155.00
4. TFS7MT (Complete Gasket set): US$77.50
5. TPR7MT: US$146.00 (Please make sure the size of piston and rings you will need, we have standard size, 0.020 inch oversize, and 0.040 inch oversize).
Gavin
http://stores.ebay.com/JIS-Engine
autoengpart@jisengine.com
Or Matt was the other supplier
Matt Junker free to call 909-229-7701
The Oil pump mod is as you said shim the spring to increase the pressure.There is a detailed link on the UK forum on this subject but the forum is down at the moment. Will post link as soon as its back up and running.