A company here in Sheffield, who supply springs to vehicle manufacturers and racing teams etc, can make any spring to any spec. They hold data on many vehicles, including uprated springs for a 100 series but don't have any for the 80 series so will need a spring to copy which makes things a bit more awkward. A ballpark figure is around £90 + VAT with possible discount for cash. Out of curiosity I phoned a main dealer for price/availability and they can get them in around a fortnight, £1024 for a set of 4. That makes the Amayama prices look cheap.