After a bit of trial and error, it seems there is plenty of availabilty until Sat 24 Oct, which is the end of the IATA Summer season. Either the route is not operating after that (unlikely), their winter schedules are not yet available (check at their website), or they have just not yet relased winter miles seats. I imagine it's the last option, and you can either contact S7 and ask, or else check back on a weekly basis. On every date I looked at, there were the maximum 4 seats in both classes on all 6-8 daily flights. I don't think there is a problem getting a seat.
For the summer season, economy is a very reasonable 4500 Avios + £5 each way, or 9000 + £5 for business.