While searching for forums hosted in iran:
the search engine query تالار گفتگو .ir seems effective
also, it's better to further check if the sites found are truly hosted in iran or not, by sites like:
https://check-host.net/
https://www.ipvoid.com/website-location-finder/
since sometimes some sites ending with .ir are still hosted in (((usa))) because of the interference of content delivery services like (((cloudflare))), and such sites must be avoided since they aren't safe from kike censorship