Jdub was referring to the fact that the 7M-GTE forum is for posting threads related to 7M-GTE specific topics. The A/C in the car is not a GTE specific topic and therefore does not belong in the forum you posted in.
As far as conversions. Toyota offers all the parts to do a conversion, but if you're looking to change/upgrade components beyond the original specifications, I don't know specifically where to get those parts.
Hopefully someone will chime in who has done some A/C upgrades on the A70.
Jeff
EDIT (Toyota Retrofit Information for A70 Supra):
88840–33020 - Retrofit Kit, R134a
88471-12070 - Receiver/Dryer, R134a Conversion Type
08885–09107 - ND Oil Type 8 (250cc), 120cc Required
90099-14120 - R134a Discharge O-Rings
90099-14119 - R134a Liquid O-Rings
90099-14121 - R134a Suction O-Rings
90099-14122 - R134a Pressure Switch O-Rings
R134a Charge Amount: 650g