Existing sinks are gifting and deck expansion (deck expansion being the biggest and not really commonly used – but that's a discussion for another thread).
I propose adding a third one: a tax on all sales. With the removal of TCALS, this would ensure that high value transactions (whether real, transfers or inflations) would carry an obligatory cost (name it what you want, tax or “artwork transportation fee” for additional lore). Of course, the tax would be proportional to the sale amount, say 10%~15%.
Consequences: mandatory sink, inflations are nerfed, a TCALS replacement for bank transfers, flipping isn't as profitable
The 10%~15% are obviously just off the top of my head, it doesn't have to be that high.
In what concerns implementation details, I think the most intuitive would be to include the tax in the price listed on the market. In other words, the buyer pays the price displayed, but the seller only gets 90%~85% of that.