First off, whether the parents are shiny or not does not affect whether the offspring will be shiny or not. The only factor that affects the shininess of the children is what language the parents are. So for the best odds of getting a shiny, I would recommend breeding a Dratini of your own language with either another Dratini of a different language or a foreign ditto (you can get a German Ditto from
most's thread, make sure to read the rules before requesting one, though. Mainly that you're supposed to post a message on his profile rather than in his thread).
I could send you a female Extreme Speed Dratini with Marvel Scale if you want. It can breed with anything that's male and in the same egg group as itself and still produce offspring with Extreme Speed and a chance to inherit Marvel Scale.
However if you don't want direct outside help with getting decent parents, you can get Marvel Scale Dratini from the friend safari. A good way to get Extreme Speed Dratini would be to get it from HG/SS and then transferring it up to X/Y/OR/AS. You then need to have a Female Dratini with Marvel Scale breed with a Male Dratini with Extremespeed.