Hi.
Very good work so far.
About the skin, you just have to measure the diameter of the mouth (the top) of the drum. Yours should measure 9,5" or 9,75", if it's a Gon Bops requinto.
If it measures 9,75", you can chose the facility and order a ready mounted 9,75" superquinto head from Gon Bops (models California or Alex Acuña), see here :
http://www.gonbops.com/products-category/congas/But everyone here, including me, will tell you it's more fun to mount a skin by yourself. Assuming you've have kept the old one to use the flesh hoop.
There are lots of places and sites where you can order some conga skins. Depends on where you live : USA, rest of America, Europe, Australia, Asia ?
Tell us more, and then we can help you better.
Just my 2 cents.