When it has been pumped up, you should get at least 70 plus shots at full power. The other way is to charge them from a diving cylinder.
BTW - be careful pumping the B. things up otherwise you'll see strange colours and stars; unaccustomed exercise and all that
There was a bizarre item floating around at a Bisley arms fair a while back: someone had managed to insert/weld/bodge an underlever air rifle into a No1. Not a bad attempt, but clearly not a factory job.
There is some sort of plastic replica SMLE made by a Japanese company - you can find them on eBay. I don't think it is an air rifle, though.
Saxby-Palmer also made a brocock-style set of air cartridges that could be fired through an Enfield; quite valuable collectors' items now - those that are allowed to keep prohibited weapons...
Bought out by Brocock IIRC. Always fancied a Galaxy or Saturn rifle not to mention the Orion revolver. Still, I've made up for it since..
I remember a hysterical news item when the converted Lee Enfield hit the market, they compared some puny little rifle denting tin cans with the Lee Enfield 'blowing up' sealed fizzy pop cans to prove how dangerous it was. Several friends took out FACs just to keep their Orions when the ban came in and now own a cabinet full of 'real' firearms as a direct consequence.