In North America: http://www.frontpanelexpress.com/
In Europe: http://www.schaeffer-ag.de/index.php?&option=com_frontpage&Itemid=205&lang=en
Front Panel Express/Schaeffer AG provide free software for designing front panels customized for your design. Any quantity can be ordered. Prices can be expensive, around $60 for a MOTM 1U format and $100 for a MOTM 2U format, especially if your panel has a lot of text and tick marks for pots/knobs. One way around this is to generate HPGL files, which can achieve the same graphic features at a much lower cost. Many art or CAD programs can generate HPGL files. One I use is Corel Draw Essentials which costs less than $100. FPE/Schaeffer AG also cuts all holes in your panel, including rectangular or other odd or difficult shapes. The black anodized panel material blends in "okay" with MOTM panels. Below is a photo showing side by side MOTM and FPE panels. The two 1U FPE panels are on the left.
The MOTM format has no visible screws for mounting of brackets or PC boards behind the panel. Non-purists can simply drill mounting holes for backets or standoffs on which to mount PC boards. Purists will need to make their own brackets. Here is one methodology:
Rack mount rails are available directly from Synthesis Technology.
Solid oak strips can form very durable mounting rails in a custom cabinet. While a metal flat rail provides the ultimate in durability, a piece of solid oak can easily support replacement of modules in the same screw holes up to 50-100 times. Drill a pilot hole for each hole location, then "thread" the location as you screw in wood mounting screws. Make sure the pilot hole is not too large. I seem to find this oak trim more easily at Lowes than Home Depot, already cut to the 1/2 inch thickness needed. Unfortunately the "1 inch thick" pieces tend to be 3/4 thick, so just buy two 1/2 inch strips and nail or screw them together for middle rails in a cabinet.
Common wood screws from your hardware store will be nickel plated flat head type. Pan head screws in a black oxide finish, to blend in with your panels, are available online from http://www.aaronsself-tappingscrews.com/. They are self tapping screws, not wood screws, but work just about as well in a solid piece of wood.
Systems using rack mount rails can use any of the rack mount cabinets from Raxxes, Middle Atlantic Products and others, available from online music retailers. For custom rack mount cabinets, try http://www.nice-racks.com/. For comparable cost to particle board cabinets, you can get racks made from solid pine in almost any conceivable stain.
Unfortunately, I know of no source for MOTM cabinets, non-rack mount format. Some information on different formats is available here: http://www.hotrodmotm.com/cab.htm. For the cost of investment in a table saw, one can make quite adequate cabinets, and relatively inexpensively as well, by using birch plywood. Cost for a large cabinet can be less than $100 for all materials. The cost is mostly your time and labor, which can be extensive.
Fortunately there are many available sources for 1/4 inch patch cables. You can get custom lengths from many online music retailers. Below are some of my favorite sources.
Peavey patch bay cables from http://www.peavey.com/ These are the best of the color molded cables that I've seen. The ohmic loss is comparable to heavier hand built cables, the cable material is thick yet flexible, and the plug finish is bright and untarnished. A six pack in six different colors runs $21.59 for three foot and $16.89 for one foot cables. You can order these online and Peavey will have them shipped from the nearest stocking Peavey dealer.
Synthesizers.com modular patch cables from http://www.synthesizers.com/cables.html . These are built for the Synthesizers.com systems but work just as well for other modular systems. Lengths from one foot to six foot are available.
Like cables, these are available from many online music retailers. Common manufacturers include Pomona, Raxxes and MAP. Cost is about $12.