[Glm]

Does anyone know the pKa for Pyridine trifluoroacetate? and what's the difference between Pyridine hydrochloride? Thank you in advance.

[Dan]

I assume you mean pyridinium trifluoriacetate/chloride? I doubt there is much difference.

[pgk]

Pyridinium trifluoroacetate and pyridinium chloride are salts and thus, the term pKa is not applied. The term pKa is applied to acids and the term pKb to bases and they are indices of acid and base strength, respectively. For homogeneicity and comparison reason, pKa can also be applied to bases, too.
The acidity or basicity of a salt is described by the hydrolysis constant Kh and the corresponding negative decimal logarithm pKh.
pka, pKb and pKh are referred in aqueous media, only. pka, pKb and similarly, pKs (solvolysis constant) have different values in organic solvents.
Question 1:
Kb = Kw / Ka
What is the relationship between pKa, pKb and pKw?
Question 2:
Kh = Kw / Ka∙Kb
What is the relationship between pKh, pKa, pKb and pKw?
Note: Kw is the water dissociation constant and Ka, Kb are the dissociation constants of the acid and base, respectively that produce the salt.

[clarkstill]

Pyridinium trifluoroacetate and pyridinium chloride are salts and thus, the term pKa is not applied.

I don't believe this is the case. The equilibrium between pyridinium and pyridine doesn't involve hydrolysis. It's perfectly valid to treat a charged species as an acid.

To the OP, this is a very useful resource:
http://evans.harvard.edu/pdf/evans_pKa_table.pdf

[pgk]

Of course, pyridinium salts do not involve hydrolysis in organic solvents but they involve solvolysis and ion dissociation depending of the solvent ionization degree. Thus:
“The acidity or basicity of a salt is described by the hydrolysis constant Kh and the corresponding negative decimal logarithm pKh………..similarly, pKs (solvolysis constant) have (has) different values (value) in organic solvents.”
Thanks for the link, that contains pKa values in DMSO and thus, it is very useful.
PS: I fully apologize for my inadequate English that may generate confusions and misunderstandings. 

[Dan]

Pyridinium trifluoroacetate and pyridinium chloride are salts and thus, the term pKa is not applied.

No, pKa still applies to salts - pyridiunium, other protonated nitrogen heterocycles, ammonium, hydrogen phosphates, hydrogen sulfates... the list goes on.

[pgk]

Indeed, pKa still applies to salts - pyridinium, other protonated nitrogen heterocycles, ammonium, etc. But pKa of a base cation measures the acidity of the conjugated acid of the given base and not the overall acidity (or basicity) of the salt. Besides, there is no need to explain why pyridinium trifluoromethanesulfonate and pyridinium stearate are not the same, regarding acidity (or basicity).
In other words, the answer in the given question is that protonated pyridinium has the same pKa in both salts (= 0.72, according to the above link), but pyridinium hydrochloride is more acidic than pyridinium trifluoroacetate.