This pattern 14 rifle should be .303 calibre, as many have pointed out. If you get a look at it, double check for any US markings, such as model of 1917. As mentioned, the pattern 14 was adopted by the US in World War One as the model 1917 and the calibre was changed to 30-06.
To answer your ammo question, 303 british is loaded by all the big manufacturers, Remington, Federal, Winchester etc. As stated earlier, avaiable in 150 grain soft point and 180 grain soft point. You can also buy UMC full metal jacket for plinking, it is a little bit cheaper and loaded closer to the original military loading, I think.
To answer your other question about being dime a dozen, there were way more SMLE's produced than P14's. However, full military configured rifles of any type (Mauser, Nagant, Enfield, etc) are getting rarer and rarer. The good old days of finding a good condition Enfield at SIR for $50 are long gone. Any enfield that shows up on the consignment racks these days is usually bubba'd.
If this rifle is in Winnipeg or surrounding area, let me know and I'll go check it out with you if you want. Be warned if you buy this, once you buy one millsurp, you will get the bug and start buying more. Milsurps are the crystal meth of gun collecting.