I think some of the funkier thrift shops in the Mission might be a good place to look. There is one on 16th between Valencia and Guerrero, on the North side of the street, that I imagine might have a cloak like that. Otherwise, try the amazing Alameda antiques market, which is the first Sunday of every month in the Alameda naval base. It is a huge awesome market and they have tons of unusual and funky clothing. You have to pay to get into the fair ($5–10 depending on how early you go) but it’s worth it. Another option, if you’re willing to pay, is call the folks who run Stitch, the DIY sewing school and shop in Hayes Valley, and see if one of their sewing/crafts artists will make you one on comission. It might be less expensive than you think, since a cloak is probably only one or two pieces and quick/easy to sew. You could also pick out the fabric yourself and get exactly what you are looking for.