I did the same thing the other night whilst redoing the blueing on a HW35
I made one from a biro pen spring, just cut the spring down to 1/2" long and open one of the coils up to about 1/4" dia. fit the wider coil into the little hole first and then put the safety in, if ithas the tendency to slip in any way and prevent the safety from sliding into it's hole, bend the wider tag end to make the spring aim towards the very rear of the backblock. that'll do it
HTH, PAUL