There are a couple of things out there that you might try. Outdoor Research makes a lightweight Gore-Tex glove called the Catabatic, designed for spring skiing, climbing, that sort of thing. Fully taped, but with a low-profile design so there’s not much bulk, and you can use them with or without an insulating liner. Not cheap, however聴$100. Still, they’d probably work very well. OR makes a mitt called the Lobster Claw Rain Mitt, a Gore-Tex three-fingered mitt/glove (glitt? mlove?). Just $42, and probably also very effective.
After that the list gets pretty short. Black Diamond makes a winter climbing glove called the Dry Tool ($60) that uses a proprietary waterproof-breathable laminate. But it’s insulated, and may be too warm for anything more than 40 degrees. And Mountain Hardwear makes a glove called the Tempest SL ($40) that uses that company’s Conduit fabric. Conduit is waterproof and breathable, but these gloves’ seams aren’t taped. Still, they won’t leak much, and with a light liner they will stay warm even when a little damp.
My own feeling is that the Lobster Claw Rain Mitt is the ticket. You can use them by themselves, or add various liners when the temperature drops.
Good riding to you and be careful out there in the rain and mud.