Are there gas ovens that come with a thermometer?

Many ovens in the US have such a feature.

However, ovens lie. Even if thermostats and thermocouples in ovens were scientifically accurate (they are not), they are positioned on the outside walls of the oven, not the center of the oven where you are actually doing the cooking. This might not be an issue if you are baking a frozen pizza (if this is the level of cooking you are intending on doing, go for it, and use such an oven), but would be a problem if you attempt any sort of finicky baking.

Don't trust the knob or readout on your oven, it isn't telling you the whole story. If you need precision, use a bulb style thermometer on the center rack of the oven. And unless you have very basic oven needs, don't let the presence or lack of a thermometer be a prime purchasing decision.

Welcome! You don't say where you are located. In the U.S., most ovens have an audible sound such as a beep or a buzzer to let you know that the set temperature has been reached. Some may have a light indicator.

However, even though most have this feature, many people still keep a separate thermometer in the oven (at least until they learn the nuances of their oven) as oven thermostats are not always exactly accurate.

I have not seen ovens with built in thermometer where I live in Indonesia. To resolve this problem with my 6 burner Imperial oven (a US make) I drilled the oven door at the height I cook at and inserted a dial thermometer with range to 500C. This is the rack height I normally cook. However using a laser thermometer and black stones in various positions there is a variation of temperature even at that rack height. The inner right side being hotter.

Leo, I was wondering the same!! Answer is that there's nothing you can trust. I use an oven thermometer that either sets on or hangs from a rack. I hang it as close to the center as I possibly can. It hasn't failed me yet. If a recipe says 350 for 30 minutes, the baked item is done just right.