It's not in stock, and if it was it would cost an obscene amount of money to get it here sometime in April.

This was £9 for both with a 24 hour delivery time, from UK parts stock.

Just wondering - did you try looking on Amayama?

This part is very difficult to find in (at least) the UK. Usefully the 17933-60B00 gasket is readily found so I decided to YOLO on another cap using that seal, the 17932-63J00 for the UK-model Swift. It's a tight fit, but it's a fit, and considering the previous cap fell off - tight is probably better than not.

DA63T part substitution 17932-67H00