The reason you rarely see hemlock lumber as such is that it's mixed with true firs (Douglas fir is not really fir) and the combo is called hem-fir in the market. Properties are too similar to separate for most uses.
From the Western Wood Products Association:
"Hem-Fir is a species combination of Western Hemlock (Tsuga heterophylla) and five of the True Firs: California Red Fir (Abies magnifica), Grand Fir (Abies grandis), Noble Fir (Abies procera), Pacific Silver Fir (Abies amabilis), and White Fir (Abies concolor). While Western Hemlock and the True Firs are sometimes marketed separately in products graded for appearance, these species share similar design values making products graded for structural applications interchangeable.
Douglas Fir (Pseudotsuga menziesii) is not a true fir at all, nor a pine or spruce. It is a distinct species named after Archibald Menzies, a Scottish physician and naturalist who first discovered the tree on Vancouver Island in 1791, and David Douglas, the Scottish botanist who later identified the tree in the Pacific Northwest in 1826. The species is known by a number of common names including Oregon Pine, British Columbian Pine, Red Fir and even Douglastree; however, the U.S. Forest Service settled on Douglas Fir some years ago. Douglas Fir is North America's most plentiful softwood species, accounting for one fifth of the continent's total softwood reserves.
Western Larch (Larix occidentalis), sometimes called Mountain Larch or Western Tamarack, was discovered in 1806 in western Montana. However, it remained for the botanist Thomas Nuttall to recognize and describe the tree as a previously unclassified species in 1834. It is one of only three conifers that sheds its needles in the winter, with new needles developing in spring. Western Larch is native to eastern Oregon and Washington, Idaho, Montana, and southern interior British Columbia. Like Douglas Fir, it is among the strongest and hardest softwood species."
Love that internet!