Retailers that sell shingles by the square

I am not sure if I understand your question since you named two home stores in the text of the question. Are you asking for more stores? I would grab the yellow pages and call home stores or lumber yrads. If you want to compare apples to apples you'll need to specify one brand.

If you are planning much of a roofing job, inquire about roof top delivery too.

Many brands come with several grades and styles too. I often start my projects with the ads in the Sunday paper.

As above,Please specify your request in more detail.
Thanks,
Ken

As ballengerb1 said, you have named a few already. Without knowing the town you are in, it is not possible to give more than to check sale papers and the yellow pages at least for places that sell shingles. I have worked at Lowe's for over ten years (Lumber/Millwork) so here are some questions that will probably be asked. You should have the answers before you go in.
1) Size of roof in square feet. Best way is to climb up on the roof, get a tape and measure each section on the roof. If climbing is not an option you can estimate this way: Get the Sq. Ft of the house. Measure the amount of soffit overhang. Is the roof a hip roof or gable? What is the roof pitch (many homes have a pitch of 4/12).
2) What type of shingles do you want? Dimensional look better than the old 3 tab but cost more.
3) How many layers of shingles are on the roof?
4) Will the new shingles be applied over existing layer or will the old be torn off?
5) Single story roof or higher (needed if the delivery will be at roof top)?
6) Type of ridge cap desired? This can be shingles, or a ridge vent.
7) Roof vents (number and type)?
8) Drip edge color?
Shingles, felt paper and nails should run between $42-58 per square (100 square feet). This does not include drip edge, vents, new sheeting or labor.
You can call a couple roofers that give free estimates. Make sure they provide a list of materials. Bring that in to the store for prices.