Well, you can't convert the chainring itself (at least not meaningfully), but a 34t chainring will fit on a crank with a 110mm bolt-center diameter. The bolt-center diameter is what determines whether a chainring will fit on the crank.

The combination of a 50t with a 34t is a 16-tooth differential, and some frotn deraillers may not have enough capacity to handle it. But most will.

Finally, you can buy a 34t chainring from whatever manufacturer, as long as they're in a 110mm bolt pattern. (Well, any manufactuere except Campagnolo. They designed theirs to be different so it's only compatible with itself. *%#holes. Although the economics of it makes sense for now.)

Manufacturers would like to (and often will) tell you that you need chainrings designed for 9- or 10-speed chains, if you're running a 9- or 10-speed drivetrain. But you don't. The indside width of narrower chains is the same as chains designed for 6, 7 and 8-speed systems, and the actual width of the teeth on the chainrings is the same as well.

Lickbike has Sugino chainrings in 110mm bolt pattern for $16.