When is the deadline for the Colorado Elk tag

April 6th,  You can do it online or mail.

If you're hunting public land, MANY tags are available OTC.  I'll be hunting Unit 45, in Sept..  I'll purchase my tag (guaranteed), when I arrive (either-sex).

Good luck.

Just double check that your particular unit is still otc as they have made many changes this year. My unit was otc but this year it's draw only.