What are the best substitutes for arborio risotto rice?
Your best replacement would be another short grain, or in a pinch, medium grain rice. (if it's a variety that doesn't cook up creamy enough for your liking ... you can cheat and after you remove it from the heat, quickly stir in a beaten egg)
And how about when your only choices are all the local shops have: pearl barley, or 'brown rice with barley and spelt blend'?
I'd probably go with the pearl barley, just because it'll have a more consistent cooking time than a blend. (so you don't end up w/ little uncooked nuggets in a puddle of overcooked mush.
This makes me think pearl barley is the best option. It take a lot more boiling than normal rice (40 minutes), so I'll have to half-cook it by boiling before adding it to my pan with stock as my risotto recipe calls for.
Don't pre-cook it. You want to toast your uncooked grains in the oil, just as you would with a rice-based risotto before you add any liquid. If you don't do this step, you won't get the same flavors (I can't comment on the texture, as I've never tried cooking pearl barley this way).
If you're reluctant to spend almost an hour in front of the stove, the period to cheat is in the middle; toast it, do a couple of stock additions w/ lots of stirring, then add lots of stock & let it cook, then once it's nearly dry go back to stirring & slowly adding liquid 'til it's done ... or use a pressure cooker