18" wheel extensions?

Hey guys, i tried searching but came up empty handed... ive looked on a few sites and have been able to find barrel exntensions for 19'' rims to give the lip a bit of a deeper look...but i need something for an 18'' set 1/24 scale.. does anyone have any idea where i could possibly find them? I dont really want to resort to scratch building them b/c i know im gona mess them up..and the wheels cost as much as the models do..

please let me know,

thank you for any input.