Some ideas here: Low Carb Thickener | Mark's Daily Apple
I'm a huge fan of arrowroot.
It's one of those eternally Primal frustrations: convenience vs flavor/health. Mark's post says it all. I had a recipe for chicken, broccoli sun dried tomato pasta... zucchini for pasta and instead of using thickeners and milk, I used full fat cream... Oh so amazing. It was funny to me how in the comments in the magazine, people had said that the cream made it taste too rich. Oh, how abused the American public is that they don't like the taste of REAL cream anymore.
The eyes of all hope in thee, O Lord: and thou givest them meat in due season.
Freedom consists not in doing what we like, but in having the right to do what we ought.
Pope John Paul II
I frequently use grated courgettes/zucchini to thicken stews - they break down to nothing, but add substance to the gravy.
Okra is a classic answer to soup thickeners. Great flavor and naturally gives the soup more of a thick consistency. Just chop, and add, including the insides. Also, okra are easy to grow in your own garden, and should be abundant at farmers markets.
If you're not averse to potatoes, their starch will thicken the stew somewhat.
If you're staying low carb, you can add lots of good vegetables, cook until softened, then ladle out a few cups, run a stick blender through it to puree it all and add that back in.
Learn to like stew a different way. It's not all about the gravy.