I hope I understand your question correctly. You want to add side/curtain airbags to a 4Runner that currently does not have them?
You can, but it will be prohibitively expensive. It has been mentioned on the forum before, some insurance companies salvage/total out a vehicle if the airbags deploy. Hopefully that gives you an idea of the pricing. The other thought is most installers/techs/mechanics probably will not install them on a vehicle that doesn't have airbags due to liability issues.