I was down in Claregalway at Eugene Geraghty Joinery
(on Tuam side of Claregalway turn right at Knockdoe)
I was in the showroom and the chap there showed me
one trend which was to put cast iron spindles on every
3-4 spindles or so. I think he had one there in his hand
and illustrated.
Might be worth giving them a shout to see if they can
provide them (or if they are not in your area then maybe
they might be able to tell you who could supply them
to you).
The reichard burbridge ones are the ones we used last year. (they were all we could find) They have 3 or 4 designs - we got them at Woodies in Galway.
Be sure to get the gap between the hand and base rail right so you don't need to cut them. We had to cut all 30 odd of them with a crappy grinder - to be avoided if possible.