I find support for big rings a pain. Most Trike, folding, and mini-velo vendors have them, but they can be extremely expensive.

If you are flexible, here are some options that won't break the bank.

61T, Ramped and pinned, $52.47

61T, Ramped and pinned, $52.50

68T, No ramps, $64

69T, Aero, No ramps $72

70T, Aero, No ramps, $73.28

75T, Aero, No ramps, $79

What are you using for the rear freewheel/cassette? Rear gear ratios?