Need Dually Wheel Help

[TheBreeze42p]

First time poster.
I have a project truck and this site looked like it would be a great help.
I'm in the process of getting my Dads old GMC 3500 truck back into service. Its not been on the road for 23 yrs.
I drug it out from the briers and had it running the next day.
Dad bought it with under 10K miles and it currently has 58K original miles.

Ok now the help I need is for wheels, it has the solid ring with the split ring retainer. It is so rusted I cant get the split ring removed.
I would like to replace them with a tubeless wheel, it has the 16" 8 bolt 6.5 with a center hole of 4 inches. Where can I get something?
TIA
Eric