... that doesn't mean it doesn't exist.
Tunisian crochet is more commonly called the afghan stitch (at least in my social/crocheting circles). Since it involves picking up loops across (R to L) and then (essentially) a crochet bind off (L to R) I don't see a way to join in the round.
A flexible Crohook (TM of Wrights) or any double ended crochet hook could be used to work the Tunisian (afghan) stitch in-the-round. I found this site about circular crochet needles/hooks.
I can visualize joining in the round by working the first and last loops together (would need on extra stitch at CO) or by slip stitch joining the starting chain before picking up the loop. You could do this with one color or with two colors. Using one color (strand) you pick up loops around, then complete the stitches from right to left (from RS of work) or more likely by turning the work and working from the inside or WS to complete the TSS (Tunisian stitch)
A Two Strand Method:
You could use two strands of your color or two colors. One strand would be used at each end of the double ended crochet hook. Using contrast color or first strand of main color, You could do any of the knitting CO methods you choose or start with a crochet chain. Once you have loops pulled up across (or CO) then you would join (slip stitch or work two loops together). Join in your second strand (or main color) and complete the stitches. The second strand (or color) would then "chase" the first strand (or color) around the work.
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Annie's Attic article on crochet on the double (alias of crohook and double ended crochet hooks) appears to give a background on these circular hooks and crocheting at both ends of a double pointed hook (straight or circular).
Let us know what you find and how your project goes.