It differs for each item and character. Sometimes characters regularly wear items from the same brand or store so I will start with that, sometimes it involves a quite a bit of Google-fu. If I'm lucky, a kind visitor will send me information!
It can sometimes take hours to find a single item which is why I can't add everyone's favorite show.
Please check out the mens and plus size tags. More womens' clothes are added simply because they wear more search-able clothing. Women's clothing generally gives me something (a certain pattern, a print, different necklines or shapes etc.).
I do not do requests sorry!
Why Not? Because I don't have time, sorry. It can take hours to find a single item, longer if I'm not familar with a show/character's regular wardrobe. The amount of requests I get every week even with requests closed would equate to a full time job.
You will find a lot of the stores I post ship internationally. Nordstrom, Bloomingdales, Macys, Neiman Marcus, Saks, Barneys, Asos, ModCloth and more.. they all ship internationally. If it is not available for a certain product/store then please use the brand and product information provided to look at the locals stores near you. You could also search for a personal shopper in your area (we do not offer these services).
Unfortunately this is the case with some items, usually on the cheaper side. A lot of items are made with "x" material and they are not concerned with getting things to line up as this would add a huge amount of time, quality control and therefore $$ to each garment. If you have your heart set on getting only the most exact replica as possible I recommend using the brand info provided to look in stores in person. You could also try eBay — but I would only rely on auctions where the seller has taken their own photo.
This is impossible without direct information from the make-up artists, which I don't have.