Taking Sylvain's suggestion in:

link

and having a wish to learn I've been looking into suitable rootstock to test with.
I've found a site which seem to sell Poncirus trifoliata and Citrus aurantium, although a bit small.
Is anyone preferable for learning?

I mostly use swingle, because it gets to grafting size quickly & produces excellent quality fruit.

Thanks, seems like they will get Citrus aurantifolia in mid-july. They however note that it's from a cutting. Not sure if that's matter if it's going to be used for grafting?
Maybe I should try one of each and see which one works best for me.

Hmm, sent them an email some time ago asking about the size. But no reply yet, so I'm not sure if it's a good place to order from.

Is there a good place in Europe to get rootstock from?