Know the Wood and Size You Want
Wood Supplies in the UK have a very useful pdf (acrobat reader) descriptive sheet of woods used for miniatures. Often the same wood will have a different name from country to country. Basswood in North America, is called Lime in the UK. Mahogany and rosewood can have completely different handling and finishing techniques depending on which tree species the wood actually comes from. Wood with Provenance is wood which comes from a particular estate, building or ship which has some historic interest. As important historic artifacts are repaired, wood removed is often sold for other projects or collectibles.
Metric to Imperial is a useful conversion tool for sites which list wood in millimeters or inches.
Modellers shipyard carry a wide range of sheet and strip lumber.
Mt. Albert Scale wood is available online or from many railroad suppliers. They specialize in basswood sheets and strip wood, sugar pine railroad ties in HO, O, S, F Z, N, TT, and G scales, Scale lumber in HO, O, S, and F (1:20.3)scales Sheet lumber in clapboard, board and batten, plain and scribed. They also have detailed scale building kits in O scale.
Northeastern Scale Lumber are known for their dolls house scale Victorian laser trims and gingerbread but they also produce: metal corrugated siding and roofing in railroad scales of G, HO and O, sheets of roof shingles, clapboard siding , board and batten siding, structural shapes, moldings, (quarter to 1 inch scale) door and window trim, shutter stock and frames, picture frame moldings, stair risers, hand rails, mahogany, cherry and basswood strips and sheets, baltic birch plywood from 1/64 inch to 1:16 inch thicknesses, mahogany ship decking (with holly inlays) and numerous other specialist wood moldings and trims for railroad and dolls house scales.
Kappler produce scale lumber and wood details measured in railroad scales of N, HO, S, O, G, F, and M( 1:13.7 or 7/8 inch scale). Their products in include clapboard, scribed sheets, boar and batten siding, dimensional lumber, railroad ties, ladders, fences and gates. The majority of their products are made of basswood (lime).
Large Scale Train Supply sell Cedar, cherry, cypress, red oak, and mahogany stripwood in 1:24 (G) scale lumber sizes also 1:24 scale diecast vehicles. The site gives actual measurement of the stripwood so you can convert the measurements to see if they have any useful for the particular scale you work in.
Midwest sell scale lumber supplies through big box stores and hobby and craft stores throughout North America. They have a comprehensive range of stock wood sizes for all kinds of scratch built projects. Their products include: balsa, basswood, aircraft plywood, craft plywood, walnut, mahogany, cherry, spruce, strip, sheets, blocks and dowels.
This really is an amazing resource for exotic woods in a variety of forms. You can choose from milled stock, rough lumber, resawn wood in strips, sheets and blocks, and laser cut maple grating. There is a wide range of exotic woods and clicking on the wood type will bring up a description and photo.
Model Expo supplies ship models and hobby tools and has an extensive online catalogue. Their products are available through many hobby shops and online shops which specialize in model ships. They sell mahogany, walnut, basswood, tanganyka, cherry, beech, strips and sheets as well as laser cut gratings and grating strips. The woods are mainly intended for ship building, so very fine strips are available (1/64 x 1/8 inch).
Borcraft specialize in dollhouse mouldings in 1:12 and 1:24 scale, door and window kits, picture frames, and furniture kits. They sell stripwood of jelutong, mahogany, oak and walnut in a wide range of sizes. Turnings (legs and posts), staircases and fittings (hinges, handles) as well as pine, mahogany and oak furniture kits are available.
They also produce a range of roomboxes. They have a downloadable catalogue in pdf format and sell online as well as at many UK dolls house fairs.
Wood supplies sell a wide selection of moldings in dollhouse scales of 1:24 and 1:12, strip and sheet woods, and miniature picture frame moldings. They also carry an extensive range of provenance wood and furniture in dolls house scales from famous buildings and ships. Their wood is available online or at various UK dolls house fairs.