I'm being asked to find the p-values for descriptive statistics. However, it's my understanding that p-values are for test statistics. If I'm not mistaken, a p-value is the probability of observing a value as extreme as the test statistic if the null hypothesis were true.
Your are correct. Descriptive statistics characterize the data with which you are working. To generate p-values, assumptions need to be generated. Assumptions are not descriptive.
Descriptive statistics do not have p-values. Hypothesis tests, which can test whether or not a descriptive statistic equals a specific value, can have p-values. Whoever asked you to get p-values for descriptive statistics likely meant for you to get a p-value for whether or not that descriptive statistic equals 0. I recommend you follow up and clarify this.
What you can do is get a confidence interval for a descriptive statistic which tells you much of the same thing.
Almost all descriptive statistics are used in hypothesis testing too. So, it's not exclusive classification into inferential and descriptive when we talk about the metrics such as the mean and standard deviation.
For instance, the sample mean is a descriptive statistic. Yet, you can obtain its p-value if you construct a hypothesis, such as $H_0: E[x]=0$, i.e. that the mean of the population is zero.