I have 2 car garage(60+ years old). On exterior of the garage there are small gaps in the space between some of the cement blocks under girding the garage. What type of concrete repair material should I buy from someplace like LOWES or HOME DEPOT? Is this something a traditional concrete contractor would work on? I already called one and they did not want to do the job. Thanks.
It's pretty much the same thing as repointing bricks, with larger units.
Remove any loose mortar, replace it and the missing mortar with fresh mortar packed into the joint, and finish the joint in one of the several manners that are customary - most likely the one that matches what you already have.
At your big box store (or masonry supply) pick up a bag of mortar mix, which is the same stuff you'd build the wall with in the first place.
You can find more information by searching for "repointing concrete block"
Masonry contractors (aka masons) may do it, [Folks who pour concrete may not do block or brick related work at all] but they may also not particularly want the job, seeing less profit and more annoyance .vs. building new walls somewhere else. That can take the form of refusing to quote, or quoting so high they hope you'll go elsewhere, and if you don't, they'll at least get well paid.
Alternatively, you can "parge" the whole surface of the wall with a surface-bonding product (mortar with fiber reenforcement - one application of which is to "surface-bond" dry-stacked block walls) - depending on the state of the blocks, that can make a big improvement in how the wall looks, and you don't have to fiddle with joints other than cleaning out loose mortar - which might be easier if it's a lot of bad joints, and might be harder and more costly if it's only a few bad joints.