A nice wife, girlfriend, or mom could make one for you. Or if you are comfortable with your manhood you could make one yourself. You can get material at Wal-Mart for cheap that would work. I am working on mine and will post pics when I am done.
I haven't worn it for too long, so I can't comment on it's practical applications lol. Right now it's on my mannequin and it looks kickass. The obvious alternative is to simply buy a vest from a fett vender. Most that I've seen have a high neck on them anyway. That's what my other suit will have.
His user name is huofist. He sells different sw items from time to time. I actually bought my t-20 heavy blaster from him for my sandtrooper gear. Nice transaction. Sort of a recluse, he lives down the street from my store and wouldn't allow me to pick it up, even knocked off shipping and offered to discount the gun $5 if he could just ship it to me. Sort of strange, but reliable...
I've seen the Huofist neckseals on ebay going for $30+ and so forth. I was at Wal-Mart and experienced a mini-epiphany.
As I've mentioned before I'm building a 'b' suit to finance my 'a' suit and needed a makeshift neck seal. Well I bought a xxxl white t-shirt for $4 and I cut out the sleeve with some extra flap and it works and looks just fine to me. It's quite comfortable, not stiff, and can be lifted to cover the entire bottom of your head, right out to your chin. I don't have any pictures but when things start to be finished better I'll try to post pics.
Felt like an idiot standing in wal-mart trying to shove my head through a shirt sleeve
I just finished making my own neck seal. The one on the vest that my mother made was too thin and would fall down once I started heating up. I don't have any pictures to post, but it's really simple, and you don't have to sew. I used some left over fabric from the vest we made (a light grey 100% cotton)and cut out a strip 6" x 20", this will be the base. Using Goop glue, I folded over and glued the top and bottom edges so the height is now 5". Then I cut out 6 pieces of the same fabric 7" x 22". Starting at the bottom edge I rolled them up and glued the outside edge down, so I now had six 20" fabric tubes. Then I glued each of those onto the base with all of the excess on one side. The excess 2" is folded over and glued onto the back (this will be the edge that shows). Use an epoxy glue to set your velcro, and your good to go. It looks awesome, took less than an hour, and I had all the materials already.