You can find Duskull only by breeding Dusclops, which you can find in the Friend Safari.
As for Tynamo, it is unobtainable.
Duskull (get a Dusclops, then breed)
And for Tynamo, if you really want one, then you can either give me a rendez-vous on my wall on a fixed time in chat room, either buy BW / BW 2, or if you have one of them, just have a static Pokemon and this may help you searching in Chargestone Cave for both Joltik and Tynamo, which you will send to Pokemon X and / or Y via Pokemon Bank.
I hope this help !