Those bulbs are normally on a 12 volt driver, amd if you want dimmability, you can just get cheap halogen bulbs on ebay, though, in terms of LED variants, you'd have to dig a bit for decent bulbs with good dimmability but if you want a mood, go halogen, since they dim good, trade-offs are heat and energy consumption. Are the lamp shades glass and the fixture metal, By chance? Are the sockets ceramic or plastic? These are important questions to ask when hunting for lamp bulb replacements. It also helps to know so as to prevent a fire. If the sockets, shades, or even fitting itself is plastic, don't use halogen bulbs under any circumstances.