high fiber dry foods that are good for senior cats ??

my younger (4, long haired) cat (who's prone to massive hairballs) has suddenly stopped pooing regularly. she gets the vets best hairball chews and that helps immensely but It's been concerning me that she's suddenly not pooing.
I tried pumpkin and psyllium husk to add to her wet food but she didn't like either. the only thing that's helped slightly is dulcolax powder I already give my 18 year old cat who's had consipation issues for a few years now due to her age.

Ive been talking about it with my dad who's a vet and he said I should be giving my cat a dry food that's over 6% fiber. the one my cats eat now (alongside wet food) is rawz air fried turkey and chicken. I love it because it's lower in carbs and only 1% phosphorus so it's good for my 18 year old cat as well but since it's only 4% fiber im going to have to find something else.

do any of you have any recommendations for high fiber foods ?? I'm gonna talk to my dad as well but I thought i'd ask on here as well.