You can buy a 8 x 8 x 100 HSS toolbit from Arc Euro for £2.96 each, £7.55 for 3 off, and £14..20 for 6 off, plus shipping
Prices include VAT
At those prices, it is worth learning how to grind a tool, to whatever form you want.
Incidentally, the ones shown in the picture earlier, although described as "Form Tool", are not really.
Something got lost in translation.
A Form tool would leave it's shape (Form ) in the work, in the way in which a screwcutting, radius, chamfer, or a parting tool does.
A knife tool GENERATES a cylindrical surface as a result of the combined rotary motion of the work, and the linear motion of the tool, or a flat surface by the same process when facing.
Turning a convex centre or a.concave, is, again, a generating process.
Round bar starts as a cylinder, but hexagon or square bar does not, before anyone says it!
Howard