Hiya! I’m so so sorry about how late this response is ><
Funny enough, I actually owned the jacket before I made the cosplay, and it was part of the reason I completed it in the first place since I had the jacket to base it off of~ XD
But otherwise for street-tier Seer hmmm, I’d look up jean jackets potentially too, if you get a white one I know there are ways to dye denim so that’s a possibility~ Cotton maybe as well? It looks like it could also be leather-ish with the elastic ribbing you can see sometimes but unless you can find it in the colour on ebay I don’t know if you can dye any of that… But a quick search on my end for white jean jacket brought up a few options so that might be your best bet~
I hope that helps, and I wish you all the luck! :D
And thank you so much <3~