I usually find what I need in a couple of days. I don't know how you guys get the millions of credits that you can waste on a mod, I can only drop like 200 crystals every couple of days for refreshes to get the mods I need. Not sure how you can justify dropping 3k in crystals for a mod, unless your dropping real money for it.
This isn't the first time I've sold a mod I was intending to keep. Normally I attach the mod first and then sell the other and use the credits to upgrade the mod. But I didn't do that this time and when I hit the gold mods I sold the one I intended to attach on accident. Mistakes happen, that's the thought process of being able to buy your mods back.