I use Bankruptbikeparts on ebay for rims , I usually buy a pair if I buy coloured.
This a single also look in their store/shop for others.
700c RIGIDA X-STAR RIM 622 – 19 HYBRID CROSS 36 SPOKE DUAL WALL BLACK | eBay
For spokes I use ryan builds wheels/ryna for spokes, he has an ebay presence but I buy direct off the website.
Hubs I have never needed to buy really as I use spares I have from old stripped down bikes but again one would have thought BBP would sell them.
Tbh though if you just want a std 700 x 19 QR wheel buy a complete one , on ebay for about £38 front or £44 for rear cassette spline.