Gunbroker.com. There are 3 or 4 honest sellers there, including Eddy Yuja who sells under the name 81MM. He has a recoil plate you could use http://www.gunbroker.com/Auction/Vie...Item=139384822
Stay away from the seller No Guts No Glory AKA m1carbineparts.com. They are two aliases used by the owner of Riverbank Armory. He uses the name "abcleigh" on Ebay, so avoid him there too.
Both the square and diagonal patterns were used when your carbine was made.
Most Type 1 bands and swivels you will see for sale online are reproductions, and real ones are rare and expensive. Don't pay a collector price for a reproduction. Consider buying a reproduction band and swivel (~$25) just to get the swivel and screw, so you at least can use the carbine until you find a real swivel and screw (good luck with that!).
Either is OK. International Silver stopped marking the oilers for each prime contractor early on, and just marked them all IS.
C-tips were used during World War II, both types were used after World War II. There are a lot of reproduction/fake C-tip slings out there, but real ones turn up on ebay, on the CMPTrader Forum CMP Discussion Forum - WW2 C tip carbine slings and at http://whatacountry.com/carbineslings-wwiiused.aspx
Don't worry about markings or dates on C-tip slings, most genuine ones didn't have markings on them or have lost them by now, and many slings with markings are fakes. Try to become familiar with the appearance of the fabric weave and the metal tips on genuine slings
The D-tip slings are cheaper and work just as well, and are correct for the Korean War and later http://whatacountry.com/carbineslings-vietnamused.aspx
http://www.gunbroker.com/Auction/Vie...Item=139384822
The screw length was the same throughout production. $2 for the screw at Bill Ricca's M1 Carbine Parts and Accessories
You can find 15-round USGI magazines at gun shows, gun forum trader boards, and on Gunbroker.com http://www.gunbroker.com/Auction/Vie...Item=139162144
As for markings, any of these would be appropriate M1 Carbine 15 rnd Magazines
15-round magazines were used during World War II. Both 15 and 30 round magazines were used afterwards. The selective fire M2 Carbine needed the increased capacity of the 30 round magazine. Many 30 round magazines you will come across are repros/fakes, stick with the 15 round magazines.
Yes, but it was often lost when the stock was sanded either during an arsenal rebuild or by a civilian owner. However, I think you should resist the temptation to pay someone to "restore" your stock by stamping a fake/reproduction acceptance mark (cartouche) on it. Putting fake marks on an otherwise genuine carbine is heading in the wrong direction in my opinion. Nothing screams "fake!" like a freshly-stamped and usually not exactly correct cartouche on a 65+ year-old carbine. The aforementioned abcleigh apparently has a bottomless, endless supply of rare I-cut high wood carbine stocks with nice clear cartouches on them, that he sells for big bucks to one-born-every-minute buyers on Ebay.
A good stripper to use is Klean Kutter http://www.wmbarr.com/product.aspx?catid=72&prodid=92 which is designed for use on antiques and fine furniture. It will strip off the poly without harming the wood. You can get it at Home Depot, Walmart, etc.
The vast majority of Inland stocks, including yours, were made by the S.E. Overton Co. (that's what the OI code means) and they dipped the stocks in raw linseed oilas a finish. As stated earlier, you can get raw linseed oil, sold as flax seed oil, at health food stores, Walmart, etc. Organic Flax Oil | Walgreens Official Web Site
The M1 Carbine is a pretty simple firearm, so you should be able to check it yourself. You might want to check the headspace, and for that you will need a bolt tool http://www.gunbroker.com/Auction/Vie...Item=139222341 and a .30 M1 Carbine Field gauge http://www.midwayusa.com/viewProduct...tNumber=522178 as a minimum, or the whole set of Go, No Go, and Field gauges. Check the bolt for cracks around the right (bigger) lug
and make sure the extractor plunger is assembled properly
and you should be good to go.
By the way, the bolt will not be held open after the last round with a 15 round magazine.