Implementation and Testing of SRP-6a
SRP protocol is quite abstract so to provide matching implementation for version 6a you need to know following:


N, g - group parameters
H - hash function, there can be different hash functions used for different values
how is private key x calculated
how is shared session key K calculated
how are evidence messages (M1, M2) calculated


In addition you need to know what is internal representation of numbers (byte order, padding) and what is the format of messages being exchanged between client and server.

Without that knowledge all you can do is reverse enginner (even without disassembling binary ie. you could deduce what might be hash function based on size of M1) or try your luck with different configurations. For example (based on RFC 5054 and SRP-6a summary):


byte order: big endian
encoding: UTF-8 (for username and password)
N = 2048 bit prime from appendix A
g = 2
H = SHA1
x = H(s | H(I | ':' | P))
k = H(N | PAD(g))
u = H(PAD(N) | PAD(B))
K = H(S)
M1 = H(H(N) xor H(g), H(I), s, A, B, K)
M2 = H(A, M1, K)


As for the test vectors I haven't found others then those at RFC 5054 and on Stanford SRP demo page.