You can get clear retainers on ebay, amazon, good tattoo places that do lots of piercings and walmart. if your getting gun pierced (usually 20 or 22 gauge) you will need at least 18g retainers which are harder to find and to be honest the cheap pack of 100 I brought from amazon which arrived on a slow boat from china after 2 months looked an awful lot like short lengths of fishing line with blobs of glue on the end. (you need plastic backs which you can also buy cheap or use the ones that hold fish hook earnings onto the packaging card)
If you go for the higher end retainers made of bioflex you may be able to get a piercing place to put them in immediately as they are supposed to be suitable for new piercings, all other plastic retainers aren't. Bioflex will likely be 16g so your going to need a needle pierce anyway and some of the options use flesh coloured ends so whilst not invisible are supposed to look more like a mole/spot etc.
For me I went with a self pierce kit from walmart, enlisted my partner to do the business at the start of a 4 week vacation, wore the gold studs for the vacation then switched to the retainers for the flight home and whenever i was around family. It was traumatic changing them sometimes and problematic doing it even twice a week. I kept this up for three months under shoulder length hair before i came out anyway, and no one had noticed when I asked. After coming out and keeping the gold piercing studs in rather than plastic ones occasionally, my ears healed nicely, possible they were at that stage anyway, but I think the swapping around and using the plastic ones prolonged the healing period somewhat.
