Buying premium packs on a PlayStation account

ever since I migrated to pc from PlayStation I couldn’t see premium packs in the research tab and I can’t buy them from the store. how can I get a premium pack now?

You can Transfer your Account to a Pc Account or otherwise you‘ll Need to buy them on a PlayStation and Login to the Game on the PS

There are two different scenarios.
If you just login on pc with a psn account then all purchases must be made on the psn account

To really migrate you need to remove the link to the psn account. This procedure is one time only and irreversible…was suspended temporarily but should be possible again in the future.