I could swear I had one

I was so upper sure that by now I had all the knitting needles accumulated that I would ever need. Ok, maybe not every length(I only use circular needle or DPNS), but every width...
Well turns out I don't or atleast I can't find it. I'm missing a 8mm needle now, which I desperately need, like right now. I wanted to start knitting a project today that already got delayed too much! And best of all? I was a 100% sure I had this 8mm needle!
Honestly, I could swear that a few months ago I needed a 8mm needle and therefore must have brought one. But maybe I ended up using a 7mm or 9mm needle instead? Anyway, really thinking about going out once more and buying one, but the nearest shop only has a small selection and you never know which they are "currently" out of...
Argh!!!

EDIT: 10 minutes after writing this I went to the LYS and brought the needles! Surprisingly they had a selection of 8mm needles, but why do they always offer the expensive needles first? Hello, me student, me not much money!
In contrast my favorit LYS 2 owner told me that a few colors of the yarn I needed for the project where destined to go into the sale bin when I asked for the yarn. She knows I don't have much to spend so volunteers this info! Actually she also suggested a different cheaper yarn!