Here is the Mancini Racing small block stuff => rocker arm shaft studs, strangely enough though it appears to be a NEW part and no price is shown.

I have been looking for non-ARP cost level stuff myself, this is for the W2 heads and so far my best match has been the Dorman stud kit, which is: Steel, Grade 8, Zinc Plated, 3/8 in.-16, 3/8 in.-24 Threads, 2.750 in. Length, Set of 10, $17

The overall length may be a tad much @ 2.750", I haven't checked yet with the shaft installed and valve covers on, seems like they look "long", but I think there is enough room there. If sizing wise this work I still need to source the nuts...so a bit more cost there.

Anyways, keep in mind, this is a 3/8" setup, I think the stock heads are 5/16", no?