http://www.monstermodelworks.

http://www.monstermodelworks.com/

Should find most of what your looking for here. 

Mold your walls

http://www.linkaonline.co.uk/

Not just brick but stone work as well.

http://www.linkaonline.co.uk/mem---james-j-eager.html  - A scratchbuilt building I finished recently done with stonework.  I'm currently working ona building with both stone and brickwork as a station.  I'm doing a writeup on it as well with lots of construction photos.

Brick buildings

Short answer is you laminate the raised brickwork over the flat portions. Depending on what types of materials you are using that could be layers of plastic or card stock scribed to look like brick or it could be modified pieces of the wall material or it could be commercial castings or formed pieces.

"One person here scribes the

   You never know what you can do till you try it. I suggest starting small, maybe  a brick BBQ or raised planter or brick walk to see how the various materials and techniques work. Skills can be developed with more hours of experience....DaveB 

Short answer is you laminate

That's how I've done it on my brick buildings. For instance:

Mine's 1/24th scale, and I scribed all the bricks. But in smaller scales you could use brick sheet for the basic stuff, and then it would be fairly simple to scribe the arches or other details on a separate piece of thin material and glue them in place.

Laser engraved brick structure kits

See ITLA Scale Models product line. 

N-scale Architects

Has very nice brick sheets in all scales, and one of their sheets includes arches and other special shapes.  For my scratch built Moscow, PA, passenger station, I used an arch and cut the opening in the siding oversize, then glued in the arch.  If you want it slightly raised, just laminate a piece of 0.010 (or appropriate thickness) styrene to the back of the arch first.  I also used an 0.020 splice plate on the back of the siding to provide strength.

Layers are key

I agree layers are key!  The pics below are from a building I have started, and sadly never finished.  Several layers of laser cut .024" thick laserboard to achieve the various thicknesses.  Lots of work to draw and figure out in cad, but pretty fun to assemble!