I can supply most spares for the following list of Classic British Bikes. Look through to see if your Classic Bike is listed.
BSA
Bantam, D1, 125cc, 1948 - onwards
Bantam, D3, 150cc, 1948 - onwards
Bantam, D5, D7, 175cc, 1948 - onwards
Bantam, D10, D14/4, 175cc, 1965 - onwards
C10, C11, C11g, C12, 250cc, 1937 - 1957
C15 250cc, 1958 - 1967
B25, C25 250cc, 1968 - 1973
B31, B32 350cc, 1945 - 1959
B40 350cc, 1958 - 1969
B44 440cc, 1964 - 1970
B50 500cc, 1971 - 1973
B33, B34 500cc, 1947 - 1960
A7 500cc twin, 1948 - 1963
A50 500cc twin, 1962
A10 650cc twin, 1950 - 1963
A65 650cc twin, 1962 - 1973
M33 500cc, 1947 - 1960
Norton
Jubilee 250cc, 1959 - 1966
Navigator 350cc, 1961 - 1966
Model 40, 50 350cc, 1955 - 1966
16H 500cc SV, 1934 - 1955
ES2, 18, 30 500cc, 1935 - 1966
Dominator 77, 88 500cc twin, 1949 - 1966
Dominator 99 600cc twin, 1949 - 1966
650SS 650cc twin, 1961 - 1963
Atlas 750cc twin, 1964 - 1968
Commando 750cc twin, 1968 - 1974
Commando 850cc twin, 1972 - 1975
Triumph
Terrier 150cc, 1954 - 1956
Cub T20 200cc, 1954 - 1968
3TA, T90 350cc twin, 1959 - 1968
5TA, T100 500cc twin, 1957 - 1968
Trophy Daytona 500cc twin, 1966 - 1975
3T 350cc twin, 1949 - onwards
5T, T100 500cc twin, 1949 - 1963
6T, T110 650cc twin, 1949 - onwards
TR6 Bonneville 650cc twin, 1959 - 1974
TR7 Bonneville 750cc, 1975 - 1982
Trident 750cc, 1969 - onwards