If JSR don't have them, do give NM a try. They might well have the FTTs you need, too.
It might also be worth ringing Range & Country at Sleaford. The last time I bought pellets there, they were very good on price. They could mail them out. Or, depending on what time you were travelling to The Bash, you might be able to collect from there - Sleaford is only about 20 minutes' drive from Newark, where you'd be coming off the A1 and going down the 46 to Neil's. Same roundabout when you come off the A1 - take the A17 (I think) to Sleaford.