Reddit mentions of The Tie Bar 100% Woven Silk Burgundy and Gold Double Stripe Tie

Amazon has a couple of nice-looking ones. Just search "red gold tie," and it'll pull up some very nice ones, like this one. Apparently the Harry Potter brand-name Gryffindor ties they sell are closer to purple and gold, not so much red and gold, so I'd steer clear of those. Same for the one in the official Warner Bros. shop - make sure to read the reviews, a lot of them are purple-ish, not red. The Universal Orlando shop has a fairly good-looking one, though I bought a Hufflepuff tie from Universal/WWOHP, and it felt a little cheap to me... still, it looks great. You might want to try getting one from them. Lastly, Whimsic Alley has been making the rounds on r/harrypotter lately, and they have lots of great costume gear. They have a Gryffindor tie that looks pretty darn good, but I've never purchased from their shop before, so I can't vouch for quality. They seem pretty intense about accuracy though (even differentiating between different tie styles in the movies), so I bet you could safely order it without worries...

I hope that helps. :)