Best online shops to find details for an ALW Phantom costume?

There are no pre-made, mass produced Phantom costumes that do not look like crap. anda will have to assemble yourself, atau commission a seamstress to get what anda want.
I'm afraid your soalan wasn't entirely clear, as well. Are anda looking for a good ALW style costume (and then anda need to specify stage atau movie), atau lebih Leroux? In the case of the stage style costume I know Phantom On A Budget offers tips to get the right look. Although, for the sequined cloak, you're going to either have to commission it atau get yourself a Bedazzler.
If you're wanting lebih of a Leroux, then I would go on ebay to look for gentleman's styles from the late 1800s. The novel berkata that he dressed in evening attire (so very elegant and fashionable), that his suit was ill-fitting, and he wore a black full face mask. If anda want something fancy, Venetian masks can be found. Papier mache would be period appropriate, atau anda could do what I did and make your own (mine looks like s**t, but it was a first attempt and it's still kinda cool
Goodwill and other saat hand atau retro stores will also be your friends.
Other than that, throw me some specifics on what anda want and I can give anda lebih detail.