It seems Channelmaster discontinued a UHF/VHF combiner/Amp a few years ago. I have one in the attic combining a low VHF and UHF antenna and amplifying it for distribution. I can't recall the model number, but this one
http://www.ebay.com/itm/RCA-Outdoor...-Separate-UHF-VHF-Amplification-/130774586388 looks to perform the same function at about 1/2 the cost of the channelmaster unit. I personally wouldn't trust anything RCA branded, but that seems to be the only choice.
A simple splitter can work before amplification. There may be some interference and coupling between the antennas that causes some issues, but it can work. And, it's easy and cheap to try.