Clicksia is now selling referral replacement credits. There is still no official announcement as far as I can see but the feature is already active.
One pack of referral replacement credits cost $5. It include 50 credits which means that one credit cost $0.1. You can buy several packs but you can't choose how many credits you want to buy.
Right now we can't buy referrals from the shop but that's probably because there are no referrals available.