A 30 gallon drum cooker uses grates like a 18.5” kettle or 18.5” WSM: 17.5” diameter.
If you had a 22.5” WSM you’d be looking for grates or accessories for a 55 gallon drum smoker, except Weber offers a readily available hanger for their 22.5” WSM already (minus the hooks; Gateway or someone else for those.) What I linked to works for what we were discussing, the 18.5” WSM.