Bounds for maximum number of code-words in a ternary error correcting code with length n and distance d?

I'm not sure I can find an explicit formula. Wondering if anyone can come up with lower/upper bounds.

The exact answer is unknown in general. One standard upper bound for $q-$ary codes is the Singleton bound, which gives $$|C|\leq q^{n-d+1},$$ and codes meeting this bound are called MDS.
$$|C|\geq \frac{q^n}{\mathrm{Vol}_q(d-1)}=\frac{q^n}{\sum_{k=0}^{d-1} \binom{n}{k}(q-1)^k}.$$ Using these keywords should get you started, there are many more results.
You can find them at www.codetables.de. Go to that webpage, and click "linear codes". They have complete tables of known upper and lower bounds for linear GF(3) (ternary) codes with $n \leq 243$.