Unfortunately, this is the only area of DIY HRT I don’t have experience in, because I was already infertile before starting and had no desire to pass on my horrible genetics (a plethora of chronic illnesses). My understanding is that you would usually go about this at a dedicated fertility clinic, so if you were reaching out to a general practitioner’s clinic, then I’d try searching for a fertility clinic instead. Depending on how healthcare works in whatever country you’re in, you may need a referral from another doctor to the fertility clinic. I’m not aware of any other method of long-term gamete storage than cryopreservation.

Here in the US, there are even private options that allow at-home collection and pre-paid shipping to a storage facility, though I imagine that’s more expensive than simply going to a local fertility clinic (I don’t have any personal experience, though).