Sent a Sports Illustrated magazine and two 8*10 photographs to Mr. Foyt on 6/10/16. Received all three back signed in black Sharpie on 9/24/16.
Used the following address:
A.J. Foyt Racing
19480 Stokes Rd.
Waller, TX 77484

Sent two 8x10 photographs and a Newsweek Magazine (5/29/67) to Mario Andretti care of the following address on 6/10/16:

MA 500 Inc.
457 Rose Inn Ave.
Nazareth, PA 18064-9234

Returned Signed 7/25/16

My understanding is that Al Unser Jr. resides in Las Vegas. He visits the Unser Racing Museum in Albuquerque from time to time.
While I do not have his home address in Las Vegas, I am of the opinion that he will sign your material if it is sent to the museum and you are willing to wait for a response.

Yes, I used the museum address

Sent 4/4/16 Received autographed photo, Sports Illustrated and Indy 500 ticket on 4/15/16 Thank You, Al!