I imagine you need this for testing? As if you are shipping to a 50Hz destination you would not need the conversion shipped with the unit?
If so, the quick solution might be to look at an ordinary VFD the output can be set to desired Hz, but the output is 3 phase (1 phase or 3 ph input ).
I am not sure how it would take to 1ph loads, if this is what you have, unless you put two loads on at once.
Also the output is 240vac, which most 50Hz destinations are.
If testing compressors, you might want to go with a higher HP rating.
You can usually pick up deals on ebay.