Sounds like it'll be the MkII? Does it have a more rounded forend, like the new guns? The MKI had a very angular forend.
The Air Arms Fields and Superdomes are always pellets that I'd be putting on the testing list. Also well worth trying the H&N FTT and Falcon Accuracy Plus.
Although I haven't tried them myself yet, the Weihrauch branded H&N and JSB made pellets seem to be gaining a very strong following.
And the H&N Sniper Light could also be well worth a try. Again, I've not tried them.
And that old stalwart, the trusty RWS Hobby, always seems to work very well in these at closer range.