You could try a medium carbon nickel/chrome/molybdenum steel such as 817M40, (EN24 in old money), New World specs. are bound to be different again but for reference the composition of EN24 is:
C = 0.35 to 0.45%,
Si = 0.0.1 to 0.35%,
Mn = 0.45 to 0.70%,
Ni =1.3 to 1.8%,
Cr = 0.9 t0 1.4%
Mo =0.2 to 0.35%
It can be heat treated up to 100 tons/sq.in. tensile if desired although, in the UK at least, the EN24t version, (40tons tensile) as supplied is readily machineable and probably adequate for this purpose.
On the other hand a visit to a breakers yard should yield a plentiful supply of cylinder studs to modify.