Are you referring to a frontloader pair comprised of separate washer and dryer units that can be stacked (which is properly called a stackable set)? Both units are serviced from the front but the top panel must be removed in order for the front to come off, which requires that the dryer be removed from atop the washer to gain access into the washer. The top of the dryer can be removed without pulling it down if there's room up there for the servicer to do that.

Or to a unitary (one-piece) washer/dryer set that is manufactured/sold in a stacked configuration and cannot be split for separated operation? This type of unit can be either a topload or a frontload washer. Both are also usually serviced from the front. The dryer is usually removable from the stack, and may require removal for some kinds of service procedures depending on the construction / design of the whole thing.

I doubt any retailers have "front serviceability" as a searchable parameter ... but I've not tried such as search.