I got some NGK BKR7E (6097), the car is now running perfectly(£10.43 a set from Partco).
I was getting a misfire on the decat until I fitted these plugs.
Partco had them in stock, do a search in the Yellow pages.
This is from MKIV.COM
Here is a list of the most commonly used spark plugs,
Stock Denso PK20R11, Comes pre-gaped at 0.043 inch (best on stock supra)
Stock NGK BKR6EP-11 (2978), Comes pre-gaped at 0.043 inch (best on stock supra)
NGK BKR7E (6097), Comes pre-gaped at 0.032 inch (best on BPU & APU supra)
NGK BCPR7ES (3330), Comes pre-gaped at 0.032 inch (best on BPU & APU supra)