I've been looking for the right kind of bridges to use in Warmaster for a while now.
Forge World used to sell quite large ones but they haven't been available for many years now.
Warmaster is an abstract game where a unit represents dozens or hundreds of warriors, so bridges are meant to only accomodate the smaller end of the base (20mm), not the facing that most infantry use (40mm). This represents the difficulty in maintaining cohesion marching a lot of men and beasts across a medieval crossing point.
Eventually I found the Hovels bridges, which were the right width and length, without any restricting earth or river parts attached which would demand you buy a river system to match.
A judicious application of drybrushing and now they're ready for use making up the battlefield!