According to press release there were only four Super Guppies made, only one is still being used by NASA.
On 11JUL2019, NASA Super Guppy 914 made a fuel stop at Little Rock Air Force Base, Arkansas:
The following pics are from February 2019, Marine Corps Air Station Cherry Point, North Carolina: 
The following pics are from May 2018, El Paso International Airport: 
Official video explainer of Super Guppy eating a Tyndall AFB, Florida, T-38 in March 2017:
The following pics are from November 2012, March Air Reserve Base in California: 
What’s it like to fly on a Super Guppy? Here’s a five minute long video to find out:
The following pics are from June 2012, Joint Base Andrews Naval Air Facility Washington: 
Time lapse video of load-up at Houston, Texas:
Boeing 377SGT Super Guppy, May 1976, swallowing the X-24 and HL-10 lifting bodies at Edwards AFB (Dryden), California:
A Guppy before it got upgraded to Super status with turbo-prop engines, Edwards AFB (Dryden), October 1962: 
MODEL KIT EC-130J GETS SPECIAL HANDLING BY NATIONAL GUARD!
WILD FIRES 2019: DC-10, IDAHO’S 911