I looked around and it seems everywhere I looked is sold out of the 5200 50C G4 pro race batt.
Found 5000 40C and 4200 40C in stock a couple places though.
Prices here are Canadian (one of my LHS)
amainhobbies has a 4200 40c in stock.
if you do a search for THP52002SP50D you might find somewhere that has the 5200 50C in stock. They seem to be backordered a lot of places though.