If you need 30DX Supra retracts, MRC should have them since they are the distributor of US.

Singapore, Hobbynet.jp also have them, but I would try Singapore hobbbies. Getting parts ordered from Japan costs more than Singapore and often about $20 more than US if they are available here.

GreatPlanes does not produce the 30 size. 40 & 60 size GP are exact copies of Supra.

Using Robart is a good substitute I guess.