Thanks for your replies guys...
well, i tried the following things
I used ttf that I was using with TTFtools and worked fine, with greek encoding. So these fonts support my national signs.
Then I used 3 different encoding files. I will give you part of them to tell me which is the best to use. But none of them did the work, unfortunately. All the files are for ISO-8859-7 encoding.
File #1
0xC1 0x0391 # GREEK CAPITAL LETTER ALPHA
0xC2 0x0392 # GREEK CAPITAL LETTER BETA
0xC3 0x0393 # GREEK CAPITAL LETTER GAMMA
0xC4 0x0394 # GREEK CAPITAL LETTER DELTA
0xC5 0x0395 # GREEK CAPITAL LETTER EPSILON
0xC6 0x0396 # GREEK CAPITAL LETTER ZETA
File #2
C1 0391
C2 0392
C3 0393
C4 0394
C5 0395
C6 0396
File #3
!C1 U+0391 Alpha
!C2 U+0392 Beta
!C3 U+0393 Gamma
!C4 U+0394 Delta
!C5 U+0395 Epsilon
!C6 U+0396 Zeta
So which is the best, or where should I find the right one?