Ok, my memory sucks. Lookign at a close up of the character art for Cid,
...eye cup goggles won't work. These look more like one of the variants of RAF flying goggles. The most common type of RAF goggle you'll find are the ones with the sharp angled lenses (as seen in Sky Captain & The World of Tomorrow). These clearly have smooth lenses. So far the closest I could find for you are,
I found those by searching for "vintage goggles." You might also try aviation goggles or flight goggles. As you can see form the original artwork the lenses of Cid's goggles are clear, not dark, so aviation goggles are your best bet.
Good luck on the costume! I've wanted to cosplay as Cid for a LONG time now (he's the ONLY FF character I'd ever consider dressing as) but I refuse to bleach my hair and don't have the cash to spend on a good
wig. I refuse to go half-assed.
PS Looking at the closeup pic, it really does appear that the shaft of Cid's spear is rectangular, ala a hockey stick