Next season - Sheffield + Ipswich Thursdays (as last season), Peterborough + Scunthorpe Sundays (Peterborough as last season - Scunthorpe moving from the Friday).
Kyle Howarth? He's the only other one I can see, near to the average we have left, that might be available.
EDIT: Welcome back to the Diamonds Lewis R and welcome to Danny P!
In 1990-92 he Averaged over 9.5 each season for Newcastle (averaged 8.3 in 1980 and 6.6 in the ill-fated 1st division season in '84). Missed out in the 2nd Div Riders Championship in 1991 when beaten in a run-off by Jan Staechmann, after both had finished on 14pts.
Top and consistent performer. The Mark Thorpe/David Bargh pairing was something to behold.
Olly Greenwood has signed for Buxton, who also ride on a Sunday, so you can rule him out. A name you miss off your list is Danny Phillips, who lives fairly locally and might be another being considered.