I'm not 100% positive if this is true for 4th and 5th gen, but if you breed a shiny you have a 1/64 chance of getting a shiny egg. When you breed with foreign pokémon (Masuda's Method) you have a 1/1639 chance in 4th gen and a 1/1366 chance in 5th gen. If you combine these two methods, if my math was done in the right way, it should be about a 4.6% chance of a shiny egg!! This is about 1 in every 20-25! I don't have any shiny and foreign pokémon so I can't tell if it would work, or if the 1/64 shiny chance is still active, so try it and tell if it works!