TMZ has learned the "Love and Hip Hop: Atlanta" star just inked a HUGE deal with Doc Johnson for her own line of sex toys ... and there's $300,000 on the line for her to become a brand ambassador -- selling casts of her butt and vagina.

Karlie's fans are gonna get to know her super intimately ... honchos at Doc Johnson tell TMZ their experts recently made molds of Karlie's lady parts, and they're turning them into sex toys called strokers.

We're told the little gadgets feel exactly like the real thing ... so Karlie's admirers can get down with her any time, any where. What a country!!!

Karlie's worked with Doc Johnson in the past, marketing some of their other products ... and after she recently became a certified sexologist -- yes, that's a real thing -- Doc Johnson brought her back to push her own sex toy line.

The vagina and butt molds took 6 hours to make ... and the sex toys will soon be retailing for about $70 a pop. Hey, that's cheaper than most dates.

Karlie's rep, KD McNair, tells us she's creating a blog to share her sexpert advice on lovemaking and relationships, and she's also putting together special packages of sex toys for men and women.