Thanks for all the replies guys!
I should have said at the start that I'm from the Australia forum, so need a place where I can order this online and ship it to aunt's address in the US, then she can forward it to me together with other US based items my wife and I order from time to time.
We don't have Ace or Lowes here in Aus, but I'll try the local hardware first and the soda bottle cap sounds like a great hack.
@Bob BQ thanks for the offer -- I'll keep this as my last resort mate!