As you alluded to, there is a limit to the data returned by @dbcolumn. So, if you are passing in more than that limit, it won’t work.
You could further segregate the data and show the user only a subset. For instance, create separate views for “Eastern Region” and “Western Region”, and have the user mae that selection first, then have the @dbcolumn field display and list the choices there. That is, if this narrows the choices down enough to get under the limit.