All the new clips are AEC (Aggressive Engineering Corp) made.
Midwayusa.com usually carries them for $1.80 each in a 5-pack, out of stock right now.
Garandclips.com storefront on Amazon (J. Brack) has them in stock for $2.00 each in a 5-pack. If you order directly from him using the mail link in Mountain William's post, the discount is significant for bulk orders ($1.00 each for 500+)
Ammogarand.com has them in stock (plus some USGI from different makers) for $1.40 each/100. They are good folks to deal with.
eSARCO.com has used GI (perhaps not necessarily USGI) clips in stock for just under $1.00 each in bags of 20.