Pick-axe handles, such as that on the right hand side of the picture, are readily available.
The type on the left are a bit more problematic, especially if you require various "odd" sizes and lengths.
My suggestion is to find a woodland owner (F.C./Woodland Trust/BTCV?) prepared to sell and fell a quick growing Ash tree (Fraxinus excelsior) which you can then cleave/quarter, or more. Look for a maximum of eight, uniform growth rings per inch. Orientate the rings so as to face in line with the tool's tips and rough out the handle while still green, with a side-axe and spoke shave, allowing for shrinkage. Drying will be quite rapid with little danger of splitting. Finish to shape, once dry, with a spoke shave and use a rasp to finish the socket end. For curved handles you'll need to find a tree with a suitably curved stem, these are often removed as part of the thinning regime as most people don't recognise their use and value. Coppiced Ash often has this type of stem.