Blues Scales for 10 hole diatonic harp, by Javier Argomedo.

Notation:
  Just the number     -> Draw  (4  = Draw 4th hole)
  Plus sign and number-> Blow  (+6 = Blow 6th hole)
  Quotation marks     -> Number of half steps to bend
                         (3'' = Two half note bend on 3rd hole)
  Number and 'o'      -> Overblow/Overdraw (6o = Overblow 6th)
  NA                  -> Not available

Circle of fifths:

         C
       F   G
     Bb      D
    Eb        A
     Ab      E
       C#  B
         F#

1st  harp pos (C for C harp):
     +1  1o  2'' 2'  2   3'   +4   (1st overblow is the hardest)
     +4  4o  5   5o  +6  6o   +7   (TOO MANY OVERBLOWS)
     +7  8'  9   9'  +9  10'' +10  COMPLETE 

2nd  harp pos (G for C harp):
     NA  NA  +1  1'  1   2'' 2    (not complete but usefull)
     2   3'  +4  4'  4   5   +6   COMPLETE, MOST USED
     +6  6o  +7  7o  8   9   +9   (overdraw 7th is hard)
     +9  10'' NA NA  NA  NA  NA 

3rd  harp pos (D for C harp):
     NA  NA  NA  NA   NA  +1  1
     1   2'' 2   3''' 3'' +4  4   COMPLETE
     4   5   +6  6'   6   +7  8   COMPLETE AND EASY
     8   9   NA  NA   NA  NA  NA

4th  harp pos (A for C harp):
     NA  +1  1   1o   +2  2   3'' (without tonic, and hard overblow)
     3'' +4  4   4o   +5  +6  6   (need overblow 4th)
     6   +7  8   8'   +8  +9  10  COMPLETE, with one bend
     10  +10 NA  NA   NA  NA  NA

5th  harp pos (E for C harp):
     NA  NA  NA  NA  NA  1  +2
     +2  2   3'' 3'  3   4  +5    COMPLETE
     +5  +6  6   6o  7   8  +8    COMPLETE if you can overblow 6th
     +8  +9  NA  NA  NA  NA NA

6th  harp pos (B for C harp):
     NA  1  +2  2'' 2'  3'' 3    
     3   4  +5  5   5o  6   7     You'll need to overblow 5th
     7   8  +8  9   9'  10  10'   COMPLETE (10' ?)

7th  harp pos (F# for C harp):
     NA  NA  NA  +1  1' +2  2'
     2'  3'' 3   +4  4' +5  5o    If you can overblow 5th
     5o  6   7   +7  7o +8  9'    uhmmm.. hard
     9'  10  NA  NA  NA NA  NA

8th  harp pos (C# for C harp):
     1'  +2  2'  2   3''' 3  4'   COMPLETE
     4'  +5  5o  +6  6'   7  7o   hard
     7o  +8  NA  NA  NA  NA  NA   

9th  harp pos (Ab for C harp):
     NA   NA  1'  1   1o  2'  3'''
     3''' 3   4'  4   4o  5o  6'    hard
     6'   7   7o  8   8'  9'  9o    you need to overdraw
     9o   10' NA  NA  NA  NA  NA

10th  harp pos (Eb for C harp): (try to play this ;)
     NA  NA  NA   NA  NA  1'  1o
     1o  2'  3''' 3'' 3'  4'  4o    VERY VERY HARD!
     4o  5o  6'   6   6o  7o  8'    HARD TOO!!!
     8'  9'  NA  NA   NA  NA  NA

11th  harp pos (Bb for C harp): (or this ;)
     NA  1'  1o  +2  2'' 3''' 3'    DIFFICULT
     3'  4'  4o  +5  5   6'   6o    DIFFICULT
     6o  7o  8'  +8  9   9o   10''  DIFFICULT

12th  harp pos (F for C harp):
     NA  NA   NA  NA +1  1o  2''
     2'' 3''' 3'  3  +4  4o  5     You need 4th overblow
     5   6'   6o  7  +7  8'  9     Complete if you overblow 6th


Comments:
You can play blues scale easily in: 
1st, 2nd, 3rd, 4th, 5th, 6th and 8th harp positions.
For more advanced players:
7th and 12th harp positions and other octaves of the listed above.
For expert players:
9th, 10th and 11th harp positions...
(just look how many bends, overblows/overdraw you need)

Take this scales as excercises... you should know how the blues scale sounds, 
so you can practice bends and overblows/overdraws.

(c)1997 by Javier Argomedo