I need a couple lenses and speedlites for my Canon DSLR. The usual online shops B&H, Adorama & Best Buy only seem to give 1 mile per $. I prefer UA miles or UR points but can work with AA miles too. I will have 3 minimum spends to meet:

Chase Freedom (5x gas stations, Kohls)
Chase Ink (5x office supply stores)
Amex PRG (2x supermarkets)

Is there any place I can buy Best Buy gift cards with one of the above multipliers and then buy my camera gear? I'm an expat living in Australia but will be in the USA next month.