Start with gunpartscorp.com then eBay and auctionarms.com
Most came with a tooth ramped iron sight.But there could be different styles depending on the age of your Winchester model 1894 rifle,such as a peep sight,a full buckhorn sight,etc.
The standard mod 70 had a Winchester bead front sight on a ramp base with a sight cover. The standard rear sight was a Winchester 22G open sight. The rifles chambered for .375 H&H Mag had the Lyman 6W folding rear sight. Model 70 National Match (chambered for .30-06 only) had a Lyman No. 77 front sight on a forged ramp sight base and a Lyman No. 48WH rear sight. All receivers were tapped and drilled for popular scope and iron sights. The Model 70 Super Grade had a Redfield full gold bead front sight on a ramp with sight cover and a Winchester 22G open rear sight. (with acknowledgement to The Gun Digest, seventh edition, 1953)
Use a punch and tap it across the barrel. Its a dove tail joint.
Requires professional appraisal.
adjust rear sight up for distance
Unless a different sight was special-ordered, it would have come with the Series 26 rear sight, which was made in-house by Winchester. sales@countrygunsmith.net
the Winchester 1890 is a fine 22 cal plinker. check with 'Gunbrokers.com' and look under winchester 1890 model for sale price
I would start my search at numrich gun parts corp.They can be found on the web.
You will need the help of a gunsmith.
Use Google and search for '1917 Enfield rear sight'. There are a number of websites that can help you with disassembly, etc. Start with www.cruffler.com
The Winchester Model 68 bolt action single shot .22 was made from 1934-46. It did not have a rear sight mounted on the barrel, but had a receiver mounted Winchester No. 96A peep sight (books at $20-40). As options, Winchester offered the Lyman No. 55W or 57ES Receiver Sights ($25-75). The hunt for old gunsights can pretty interesting. Lyman is still in business, and may be of some help. Good luck. By the way, the rifle (with sights) books from $275 at 100% to $50 at 60% condition.