Unless you absolutely nead a pet genderswap i would advise you to just breed the parents again if you can, otherwise during festivals, especialy when there is a 'winter wonderland' type game items like genderswaping and prismatics filters as well as restricted mutator can be sold for relatively cheap, i don't think they would drop under 50k tho.

The problem with half the eggs I have, their parents aren't mine. The egg was either given to me or I won it.

if they are themmed or project offspring it woudn't be too difficult to get one with the oposit gender, keep in mind that if they were already breed you won't be able to use the filter. ^-^