If you know how to sculpt you can make the avatar outside of SL using a sculpting software and then you can import it to SL, but I have a feeling that is not what you want.
Usually if you want to change your avi, you buy the items, shape, skin, clothes etc. from many content creators by visiting their stores or by going to the Marketplace online.
As for the Gryphon avi you can see this one https://marketplace.secondlife.com/p/Gryphon-Avatar/56786 I own the adult and the smaller ne both and I love them, they are the best Gryphon avis in SL.