Is there a such thing as just pure hyaluronic acid for fillers?

Hyaluronic acid fillers are the most common type of fillers utilized in cosmetic medicine. With that being said there are several brands produced by different companies utilizing different technologies. The goal is to achieve certain properties tailored for each area of the face or desired effects. As an example, fillers used in bony areas like jaw and cheek are "harder" than the ones used for under eye for example.

That is a bit of a confusing answer to a straightforward question.
Most HA fillers on the market have Lidocaine mixed with the HA in the syringe. Major brands in the US are: Restylane, Juvederm, Belotero, etc.
There are other fillers on the market, that are not composed of Hyaluronic Acid, like Radiesse and Bellafill. Additionally, there is Sculpta, which enhances collagen stimulation but isn't really a filler.

It all depends on the purpose and location of filler use.
In general, there is always a brand for a Health Canada approved filler. Under one brand there maybe different classes of fillers. Everything is labeled. You have the right to know. The physician is required to record the exact material used as well as the expiry date and lot number of the product used. The physician should be proud to tell you what they are using.
On the topic of "pure". That's suspect. Most of the higher concentrations used as fillers are generally 25mg/ml. That is only 2.5% hyaluronic acid. This information is readily available.
Most hyaluronic acid fillers nowadays are crosslinked for longevity. That is to make the body longer to metabolize the product, giving you a longer result. Very few or percentage are free hyaluronic acid chains unless used for skin quality injections or topical applications.
Given the limited information you received, it may a good idea to get a second opinion or at least clarify with your provider.