Where can I find a 110V/60Hz to 220V/50Hz voltage converter
If you were willing to use a 12V DC supply you could use an inexpensive inverter designed to produce 220 V/50 Hz from a car battery. Here is one available for $38
which has a sign wave output and will handle 400 watts continuous, you did not state how much power you intend to draw.

Obviously this could be run from a standard 12 V bench supply with sufficient capacity, perhaps you have one already?



Added:        The above solution is "off the shelf" and is a good one for lower wattages. As wattage increases the current required at 12V becomes annoying to handle. 24V units are available but even that becomes a compromise.

A potential solution is to use an existing 12V-230V inverter but to disconnect the 12V-230V portion and just use the HVDC to HVAC portion. 

Many low-V DC to High-V AC inverters use two stages.
 LVDC to HVDC then HVDC to HVAC.
 In many cases, using a 12-230 inverter you can implement an HVDC power supply and feed it into the DC HV rail in place of the LVDC/HVDC.
 It is far easier to implement a say 300 Watt DC power supply from 110V mains than to build a 12V, 30A power supply. 

As wattages increase the build rather than buy option gets more attractive, so it depends on your Wattage. If it's eg a power tool or incorporates any sort of a heater, then  building will probably be very attractive. 

If the above is enough of an answer and/or for more help on this consider asking here