No problem... There is not one simple api but here is the process i followed:

• Fetching the period via the season end date:
  start = https://api2.splinterlands.com/season?id=156
  end = https://api2.splinterlands.com/season?id=157
• Fetch all players from all survival leaderboards (0 = bronze, 1 = silver, 2 = Gold etc.)
  https://api2.splinterlands.com/players/leaderboard?season=157&format=survival&leaderboard=0
• For every player fetch all sm_claim_reward hive operation via the hiveengine/beem python library for the specified period
• For every received operation fetch the 2nd layer information from spl with https://api.splinterlands.com/transactions/lookup?trx_id=XXXX

Put all balances in a dataframe (table)

There you have it, for ~290 accounts it took about 1,5 hours to complete (there is backoff strategy from splinterlands to not overflood it with request)

@vugtis or others.. If you would like the python scripts i can setup a repository to download it...