In terms of salmon flies, i'd say you'd be very hard pressed to find any flies from the victorian era in a worth while condition, if you did you'd have to pay an arm and a leg for them, and even then, the best part of the fly would be the hook.
A lot of todays tyers, when they find such flies, strip them and retie patterns on the old hooks.
In terms of streamers, there certainly are a few by stevens and others who come up for auction on ebay and other places once in a while, and again, you'd have to pay top dollar for them. A stevens Gray Ghost recently sold on ebay for $220, and today there is one for sale with an asking price of ~$1500. Most flies are in the hands of collectors, and if you do get some for sale they are either not know to be from a tyer worth collecting and you might steal a bargain, or they are priced accordingly.
You mention streamers365. There are certainly a number of quality tyers who's flies are featured on the project, including some members of this forum (i'll let you figure out who). Of those that i am aware of, if you are interested in collecting some of those flies from contemporary tyers of classic patterns i'd suggest the following
Don Bastain
Davie McPhail
Bob Frandsen
Mike Martinek
Chris del Plato
Ted Patlen
Selene Dumaine
Ryan Houston
Alan Petrucci
Mike Boyer
David Mac
Charlie Mann
Jim Warner
The streamers365 flies are auctioned off the first sunday of each month, running as 7 day auctions. I bought a couple at the start of the project, but lately, as the year has gone on, the prices have increased accordingly....I didnt pay more than $20 for my flies (each), now you're hard pressed to find one under $20 - A Mike Martinek Streamer from the project sold for $87 earlier in the year, and some recently have gone for $63, Davie McPhails Jock Scott, and others in the $40-60 range too.
Another note on antique or vintage flies... A lot of flies listed on ebay and auction sites as antique or vintage, are actually neither. The best way identify such is they either have a period packaging and the tying is consistent with such, and/or they hooks on which the flies are tied are easily identifiable as vintage or antique. If you learn what the hooks looked like say 50 years ago, compared to todays hooks you'll know for certain if the fly was tied 10 years ago or 70 years ago. One example here is mustad classic hooks vs their modern 'signature' hooks. - the barbs and indeed the nomenclature of the hook model is totally different. the classic hooks have a HUGE barb, and were designed long before the dawn of catch and release; the hooks often come in little cardboard boxes or wrapped in paper. Of course, these are just hooks, but if you can access some, you will see what i'm talking about in terms of looking out for vintage quality flies on vintage hooks.
One caveat here is the aforementioned classic flies by modern tyers on vintage hooks (many of the flies on streamers365 are tied on vintage hooks, many of which are no longer made!!). Those flies will have a luster and quality about the materials that you wouldnt necessarily see on a period fly, and should be treated as such....just a new fly on an old hook
Identifying hooks is a good way to also determine trout and bass flies from yesteryear, particularly those tied on blind eye hooks (like salmon flies)- the quality and condition of the silk gut is another indicator of age and thus authenticity, but must also be taken with a grain of salt as the modern day 'hook stippers' also leave on the vintage gut to give an aged look to their new flies.
