Yes you can buy and purchase Walmart Stock by going to Computershare or contacting Computershare at their phone number which is 1-800-438-6278.
You can also purchase stock in Walmart through Walmart's transfer agent, or through any authorized brokerage firm.
Just be sure you know what you're doing when in investing in stock or anything else which goes for Walmart Stock and any other stock as well because you can easily lose money in the stock markets if you're not sure what you're doing.
But investing in Walmart Stock is almost always a good idea as long as you know what you're doing.