In core, the series Kilroy (1998) has only 1 cover, #1C (by Joe Phillips)
Here are 2 other covers for #1:
#1A (John Cassaday)
#1B (Tommy Lee Edwards)
There was also a second issue that as far as I’m Aware had only 1 cover
Also, the series you have listed as just Kilroy (Caliber 1999) is generally called Kilroy: The Origin.