You should add the solution joel_ published to your request, not only hinting on the issue. That could speedup coinmarketcap a little. The formula is precise enough for at least several next weeks (the coins/day isn't constant, but on a known decline rate)
yep, I am working on simple stats page for DCR - but more precise than approx. calculation = it will be connected directly to chain through dcrd web socket rpc and will expose simple call for actual amount of coins in existence (e.g. REQ: /dcr/v1/availableSupply ... RES: 1662000.00000000), so e.g. Coinmarketcap or others can use it.