You could try a supplement, but it's doubtful whether much of it would get to the brain. Research on GABA is rather limited so far. Still, these seem to be the foods that contain the most of it, if you want to try upping your intake:
"Foods with GABA concentrations in excess of 100 nmole per g dry weight included: brown rice germ, brown rice sprouts, barley sprouts, bean sprouts, beans, corn, barley, brown rice, spinach, potatoes, sweet potatoes, yams, kale and chestnuts. Cereals included: brown rice germ, brown rice sprouts, barley sprouts, bean sprouts, beans, corn, barley, and brown rice and had GABA concentrations of 718, 389, 326, 302, 250, 199, 190, and 123 nmole per g dry weight (DW), respectively. The vegetables: spinach, potatoes, sweet potatoes, yams and kale contained 414, 166, 137, 129, 122 nmole GABA per g DW, respectively. The GABA concentration of chestnut was 188 nmole per g DW"
https://www.dbpia.co.kr/journal/article ... DE00637183
This contains a guide to low-glutamate foods:
https://aci.health.nsw.gov.au/projects/ ... tamate-low