I am assuming you are playing either ORAS or BW2, the latest Pokémon games both without Smeargle and with the only possible non-Smeargle parent for Memento. If I am wrong please let me know.
Remember that in BW2 and before, only the male can pass down egg moves, so it is impossible (I'm pretty sure) to get Reversal and Memento on one Diglett without Smeargle.
Breed one of the moves onto Diglett. I'm going to start with Reversal, but either is possible. Diglett is in the Field egg group. You will want to breed it with one of these Pokémon — Growlithe learns it the earliest. Breed a female Diglett with a male Growlithe that knows Reversal and the offspring should as well. Keep cranking out eggs until you get a female.
To get Memento onto Diglett, you must breed with Stunky or Skuntank (or a Smeargle/Zorua/Zoroark, but you don't have access to Smeargle and Zorua only gets Memento as an egg move). Breed your Reversal Diglett with Memento Stunky and their sweet children should know both moves. Remember one again, only the male can pass down egg moves in BW2 and earlier.
I hope this helps! If you have any question please ask :)