They might still fit\, not sure. if one with screw cap one doesn't is the only differences. wouldn't be a problem.
as far as rods, ebay is the cheapest, especially with NOS. 1/8 rods are pretty thick. make sure your welder can handle that. 3/32 or 1/16 might be a bit better. and any material except aluminum or some weird titanium you can't weld with DC tig.
ER70S is common for steel you can get them at HF for pretty cheap if 1lb is all you needed. about $12.99. better price at Ebay.
ER80 or ER90 are more for chrome moly, some bike builder from Texas sells it a pretty good price.. at ebay.
ER309 is for 400 series stainless or mix stainless 300 series with 400 series.... or mix stainless supposedly good for some cast iron
*ER308 is for 304 stainless.
ERCUSI-A
NI99
NI55
are pretty expensive like 200% more than few months ago.
I just got a 10LB ER309 for $60 shipped. that is pretty normal price, about the same before pandemic and tariff pricing.