I would like some input on the basic rims I could replace my standard 12" rims.

---> Can I replace the 12" rims with a
13" rims from a Nissan C22 Vanette van?
---> Should I just maintain the 12" rims
which I worry about tyres not being
produced for 12" rims?

where you frum??

over here in Canada we have no trouble getting 12" tires(tyres) or rims.... Are you talking mags/aluminum rims or just regular steel ones?

1979 Skyline steel rims bolt up no problem 14 inch and the offset is perfect!
You just have to run 60 series tyres to keep it close to the original diameter

alex2009 ---- > Malaysia

Well over here I think they are gonna stop producing 12" tyres the 175 types because not many B310's on the road left...

Well I just want regular steel ones. I actually am trying to restore the Datsun back to some what original look but with a "compilation" of other nissan cars or parts.

Over here in Australia, the Sunny [B310] came with 13" wheels. Have a look at any 510, 710, or A10 model. We knew them as Datsun 1600, Datsun 180B & Stanza models, but they probably have diferent model numbers names there.
These all came with 13" wheels on the Australian version & probably elsewhere as well. There should be a range of stock & aftermarket wheel covers available for this size too.

more cars than just datsuns use 12inch rims... even mazda 121's still used 12 inch rims... manufacturers may reduce the ammount they produce but there are always some manufacturers that produce them on a big scale.
In india, china and asia... alot of moped style vehicles use 10 and 12 inch tyres still.

!3inch tyres are nowdays cheaper and more readily available though... economies of scale.

I buy good second hand tyres as anything second hand (with good tread and branding)is better than anything in 12inch originally fitted to our cars in cross ply construction.

Well the thing is, some people look at Datsun as contractor's car because the contractors mainly use 'em to visit construction site.

Of course some look after 'em well.

I just hate when I cant really get a certain parts, e.g. front n rear bumpers where I had to use a modified newer datsun bumpers which are cromed ones. The original were the PVC/Rubber type.

But like you say, 13" rims are standard in Australia. So if I manage to put in 13" rims, there won't be such a significant different in speed or when trying to park or make a u-turn which is so easy on 12" rims.

Provided you remain close to the original rim and tyre diameter by using lower profile tyres as you increase rim size, there should not be a discernable difference in speed, parking or turning effort.

my datsun came with 13" alloy rims with the datsun badge because it was a left hand drive one for the american market