May I strongly recommend that you first order 18 inch Strida hubs for the planned wheel set?
(You did notice that you need 36 holed hubs for Alex Y303 rims?
16" Strida hubs are 24 holed, you’ll also need spokes, nipples and rim band.)
Please let me know… 
Naturally, here’s the source list for:
the first (radial) set:
http://www.pedalkraft.de/felgen.htm
2 rims 16"/36H 70 €
72 spokes + nipples 28,80 €
2 rim bands 5,90 €
shipping D - A 17 €
the second (radial) set:
16" rims
http://www.dasfaltrad.at/
spokes + nipples
http://www.komponentix.de/
added for the 18 inch wheel sets:
18" Alex Crostini and DV15
http://www.simpsoncycles.co.uk/product.php/2202/birdy_wheel_rim