Not much need for them, either. As long as you have an HDMI output (or a DVI output with a passive HDMI adapter cable), there are HDMI-to-SDI converters. Blackmagic sells 'em for like 70€ apiece - I've disassembled one, it's essentially a HDMI decoder, an FPGA that does the protocol translation and an SDI encoder/transceiver.
Not much need for them, either. As long as you have an HDMI output (or a DVI output with a passive HDMI adapter cable), there are HDMI-to-SDI converters. Blackmagic sells 'em for like 70€ apiece - I've disassembled one, it's essentially a HDMI decoder, an FPGA that does the protocol translation and an SDI encoder/transceiver.