where to get a flex nib fountain pen?

[bjai]

I need one for copperplate writing and the vintage flex nib are not available where I am...

[tandaina]

Then you'll want to buy dip pen nibs and a holder. Cheap, available online, and if you mess them up you aren't out anything. There are others here who can give you more specifics.

[sparkinflint]

should this be in pens in general or help?

[RuiFromUK]

Great advice from Tandaina.

Dip pen nibs and holder are usually available in online shops like this one

http://www.scribblers.co.uk/acatalog/Copperplate.html

In UK they are also available in art materials shops.