If you have high enough crafting skill and rank (lvl 28 with the test passed), you could simply go into contract with a guild, earn some guild points, and then redeem them for a crystal of your choice.
If you don't have crafting skill that high... well, you'd be rather limited on what you could craft regardless of your crystal. "Here, honey, this signed Bronze Cap is a symbol of my love for you!" Hmmm, a signed Flute might work though.