They are everywhere
Here are the blues scales.
- 1 2 b3 4 5 6 (b)7 8
- 1 b3 4 5 (b)7 8
There are various ways to alter the pentatonic scale with at least one passing tone, and perhaps the most used alternate scales are the two blues scales:
1 2 #2 3 5 6 8 where the passing tone is #2/b3.
Then we have the other form:
1 b3 4 #4 5 (b)7 8, where the passing tone is #4/b5.
Here is a little piece I wrote using major blues patterns in the right hand and a typical blues pattern in the left hand. The LH intervals form the outline of X, X6 and X (b)7 chords.
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Thumb Slip Blues
Here is a PDF of some major and minor blues scales in all keys. I’m giving them a separate place, but they are also altered major and minor scales.