Your best option is to try a 1980s 110BCD triple and you can use it as a compact double. There are lots of these out there (bins full of them at the used bike places around here).

First pick up a shimano HG 6 speed freewheel in the appropriate range desired and a shimano HG chain 6/7/8 speed chain. Just changing the chain and freewheel will blow you away in how smooth your shifting becomes.