recommend XM719's
I'm pretty sure the A319 is a 700cc rim, so think your LBS is confused.
I recommend the XM719 (replaced the F519 and 319 rim) as the best match in a Mavic 26" rim with the LHT. It's a little wider and beefier than a 717 (replaced the 517 and 317) yet narrower and lighter than the XM721's (the beefiest 26" rim mavic makes for rim brakes). Can't say if it's better than Alex, but I can say that a handbuilt wheel is better than a machine built wheel. Recommend you go XM719 with double butted spokes and alloy nipples and save your partner some rotational weight whilst building a strong wheel.
Anyways, I've built at least 4 wheels with 719's and am really happy with their durablity and quality.