As Edward said they're in stock at SDS imports website. But id also look at the p226 Mecgar magazines ( which will also work with this pistol)
18rd magazines in stock at buds here
budsgunshop.com/product_info.php/products_id/54266/mec-gar+mgp22618+sig+p226+magazine+18rd+9mm+anti-friction />-------------
More options In stock here
topgunsupply.com/magazines/sig-sauer-magazines/p226-9mm.html

Steven, here >>>> sdsimports.com/sdsimports-px9-18rd-magazine-p/px918m.htm .....Have a great day!

Steven, the PX-9 and the Sig P226 magazines have identical bodies and the P226 mags run 100% in the PX-9 : budsgunshop.com/product_info.php/products_id/54266/mec-gar+mgp22618+sig+p226+magazine+18rd+9mm+anti-friction --------------- Original 18rd mags are here : sdsimports.com/sdsimports-px9-18rd-magazine-p/px918m.htm

Hi, sdsimports has 18 round magazines in stock for 35.95. hope this helps.