First Appearance Lando Calrissian

Like Boba Fett and other characters who debuted in The Empire Strikes Back, the first comic appearance of Lando Calrissian was not in the pages of a pamphlet-sized comic book.  The first appearance of Lando Calrissian was in the paperback-sized Marvel Comics Illustrated Version of the Empire Strikes Back.

Marvel Comics Illustrated Version of The Empire Strikes Back - Marvel Comics, U.S. (May 1980)
1st printing of art containing 1st appearance of Lando Calrissian in comics

This art is used again in the magazine-sized Marvel Super Special #16 and the treasury-sized Marvel Special Edition #2: The Empire Strikes Back.

Marvel Super Special #16a - Marvel Comics, U.S. (1980)
2nd or 3rd printing of art containing 1st appearance of Lando Calrissian in comics

The first appearance of Lando in a traditional comic book is Star Wars #43 with a cover date of January 1981.  This comic contains the 4th printing of the art containing Lando Calrissian in the U.S.

Star Wars #43a - Marvel Comics, U.S. (January 1981)
Newsstand
4th printing of art containing 1st appearance of Lando Calrissian in comics

Star Wars #43b - Marvel Comics, U.S. (January 1981)
Direct
4th printing of art containing 1st appearance of Lando Calrissian in comics

I love how everyone has their gun out on this cover!  The Cloud City background looks like a city found in the Flash Gordon comic strip whereas the interior art more closely resembles the Cloud City look from the movie.

Lando appears on several foreign comic book covers before his first cover appearance on Star Wars #43 in the U.S.  His first cover appearance is on the British The Empire Strikes Back Weekly #119.

The Empire Strikes Back Weekly #119a - Marvel Comics, England (June 5, 1980)
1st cover appearance of Lando Calrissian

The Empire Strikes Back Weekly #119 only contains a head shot of Lando which is taken from the splash page of Star Wars #43.  The cover blurbs reads All Your Favorite Star Wars Characters followed by Plus Their new Friends and Foes!  Since Lando is the only new character shown on the cover, this must be foreshadowing for the events to come in the story!

Another comic that pre-dates Star Wars #43 that has a more prominent Lando Calrissian cover appearance is The Empire Strikes Back Weekly #132.

The Empire Strikes Back Weekly #132a - Marvel Comics, England (September 4, 1980)
2nd cover appearance of Lando Calrissian

On this cover, Han Solo is decking Lando for betraying them to the Empire while Leia and Chewbacca look on.  Additionally, it looks like either Imperials or Cloud City Security is overseeing this mishap.  This cover, along with many of the covers on the British The Empire Strikes Back adaptation, is original art provided by Carmine Infantino.