Hand-held battery packs are rarely available from anyone except the manufacturer. I can't find sparkrite either. However, it is often possible to diy with packs. I have done on several occasions. Rules are:
1 open the pack very carefully. packs are usually a tight fit and having to glue them up will probably preclude you getting them back in the HH.
2 use the same sort of cell - ie nicad for nicad, not nimh for nicad (different charge regime)
3 use tagged cells as replacements
4 note carefully how the temp sensor is wired up (or put the fire out yourself!)
5 emery the tags and tin them so that very thin solder bonds can be used. (commercially, they weld these)
6 be very careful with the insulation components - there is rarely room for a 1mm error.
Try the following also: www.
countybattery.co.uk (say they do re-furbs)
hope this helps