This is quite simple multisolution redox equation.
You can treat KClO3 as a mixture of K2O and Cl2O5
K2O + Cl2O5 = 2KClO3
Both K2O and Cl2O5 react with HCl
K2O + 2HCl = 2KCl + H2O
Cl2O5 can react with HCl as oxidizer, but depending on (allowed) molar ratio of ClO2 to Cl2 you would to produce, in different proportion Cl2O5/HCl
eg:
Cl2O5 + 10 HCl = 6Cl2 + 5H2O
Combining two reaction
K2O + 2HCl = 2KCl + H2O
Cl2O5 + 10 HCl = 6Cl2 + 5H2O
we obtain
2KClO3 + 12HCl = 2KCl + 6Cl2 + 6H2O without ClO2
in this case all coefficients should be divided by a factor 2
KClO3 + 6HCl = KCl + 3Cl2 + 3H2O
other example
3Cl2O5 + 14HCl = 8Cl2 + 4ClO2 + 7H2O
complete reaction
6KClO3 + 20HCl = 6KCl + 8Cl2 + 4ClO2 + 10H2O
and finally
3KClO3 + 10HCl = 3KCl + 4Cl2 + 2ClO2 + 5H2O
and so on
Borek method is equivalent to mine