Fog light questions really should go in the Accessories forum...
Regarding rewiring the fog lights to operate independent of the headlights, refer to this yotatech article for possible ideas:
http://www.top4runners.com/ja/electrical.html#fogmod
As for the replacement lenses, What year 4runner? Look at this link and contact the folks at performance products. They can supply replacement lenses for the older square hellas, without the entire fog light kit:
1996-98 4Runner Hella Fog Lamp Kit
Complete kit matches OE fog lamp installation
<B>Replacement lights available separately</B>
REF # 1053 Price: $149.95
LINK:
http://www.performanceproducts.com/P...producttype=20