Sarah,

Micca is right I do have a grailla which is pitched in G and just as loud as the bombarde. I also have a bombarde in high D but they are very hard to play (perhaps not if you ar an oboeist). If you looking to play historical music as well have you considered a musette? They come in D (low) and are similar to an oboe. I think they can be played with or without windcaps and blend in with other instruments more easily.

I think bombardes are great but they are really outdoor instruments and sound best (IMO)in pairs (kan han diskan?)or in bands (bagads).

Another possibility is to look outside European culture. There are Indian instruments which are similar so you could try Jas Musicals (I think) in West London and who have a website.

I once bought a Chinese shawm from Ray Man's. He has a shop in Chalk Farm Road and used to have one in Covent Garden. I don't know if he has a website. Chinese shawms come in several sizes.

You may have to mess about with the tunings on the Indian and Chinese instruments but they are probably far the cheaper option.