gyozadude

1st rant - possible solution - buy the finished bike, take it home, disassemble the thing, and rebuild it yourself. Substitute parts as desired. Gets you a custom bike, and spare parts to boot.

2nd issue - possible solutions - first try different depth of insertion of the pump head. Try shallower, just a bit past the threads for the presta cap. This might seal just fine. Next try deeper insertion with pump head. If those don't work, get a presta-to-schrader adapter, and pump using schrader. If the grommet works on other tubes just fine, then I'd say the last resort would be to swap the tubes. But maybe the grommet is worn and if the pump is unable to hold high pressure. I usually pump with just one arm and my feet on the base of the pump. So alternatively, use the other hand and keep the pump head on the valve.

Personally, have I run into this problem? Never. But I only have been using standard Silca floor pumps, or TopPeak Joe Blows, a Japanese old Maeda floor pump, and a Nashbar floor pump and with exception of the silca, all of them had levers on the heads to lock and compress the grommet around the value. And I stock extra grommets too. I guess I've been lucky.