I have only been able to find Jobes Tomato spikes at our Ace or True Value Hardware stores. They come in small bags, 18 ct. I think. They are $2.69 per bag here. You will find them with their other plant and garden fertilizers and products.
Last year our Lowes had big bags of Vigaro brand tomato spikes. They were 50 to a bag and much cheaper but they did not have them this year. You might check your Lowe's store if you have one near you.
Jobes actually does make fertilizer spikes for aquatic plants but I have yet to find these anywhere.