Just checked Ebay, nothing, a T shirt with a 2" x 4" Red Mage and a pin, the rest plastic game pieces.
Perhaps in parts, hat, cape, the full costumes for others came out of Hong Kong, priced in AU.
That looked cheap, not real Red Mage quality. Nothing good enough for our RedMage.
Figure it out, good material, and learn to sew. Cut, pin, baste, and get someone to machine sew it.
First it takes obsessive drive to do something right. You have that. It takes a personal goal, you having the best Red Mage costume. Not something for Holoween, but for day to day wear.
At the anime fan gatherings, costumes run $1000, custom made, plus transportation and hotels, and the cost of getting in.
You are not the only Red Mage fan, other FF, I live in New Orleans, half the city costumes for Mardi Gras, some cost $10,000.
Fabric comes cheap, learning does not take long, and there is no source of quality costumes. I would think good ones would sell for $300. Patterns are easy to scale up or down, there is a place for you in this world.
My quick market study shows a demand for higher quality costumes than are available.
I make my living from my hobbies. FF is classic, good for years.