If you need printer ink for poster and banner printing, whether it is for a new printer or one that has been in your use for some time, you have a good chance of finding what you are looking for with an online search now. The first practical step is to look up the printer brand and number you are using or are considering buying.
Vendors can sell ink cartridges separately and display them on websites where they are easy to find. However, in some cases you will first see printers that go with the cartridges or even services that offer to print your banners or posters for you. If you need help locating cartridges even after reading information available to the public, you can contact a professional directly.
Because you are only one of many consumers of printer ink, few, if any, situations that involve the location of a specific cartridge happen for the first time unless the cartridge was only recently developed. Discussion forums provided by printer ink websites allow you to get information about cartridges from other consumers practically in real time. If you post your questions and explain with details, the answers you get will be more likely to give you a reference point that you trust and help you save time shopping.
There is also a possibility of using an inkjet printer for poster and banner printing. If you choose to complete the task this way using a single sheet of paper, you should use specialized software, make sure your printer can use sheets that support the use of large formats and be aware that black ink is notably cheaper to use than color ink.