Many agencies offer to get the card for you, and depending on the fee that they charge it might even be worth it. Personally whenever I need one I have just walked down to the office. The first thing to keep in mind is that Nepali government offices have abysmal hours, often opening late in the morning and then closing in the early afternoon. Staff can also be light around noon as people have lunch. Currently the TIMS desk at the Tourist Information Center is open from 9AM to 3PM. If however you need to get a permit for the Annapurna Sanctuary, that office is only open from 10AM to 2PM. One can only pray that they plan on expanding these hours and personnel for Nepal Tourism Year in 2011, but I'm not holding my breath.
Before you set out for the office be sure you have your passport, 2 passport sized photos and the equivalent of $20 in Nepali Rupees. Even though the price is always stated in US$, they only accept Rupees, so make sure you have the correct kind of cash with you. Also on some occasions I have been asked for a copy of my passport, including the page with my Nepali Visa, and other times I have not needed it. It's not a bad idea to have a copy with you while you're trekking anyway so I'd advise to make the copies ahead of time, and if they don't need them then you have another backup. If they decide there that they do want a copy, they have a copier on site, assuming that there is power.
So where is the office?
Here is a closer look;
The people at the Tourist information office generally have a good grasp of English and have for the most part been much more helpful than other government offices. If you have questions, and they are not overwhelmed at the moment, they have always helped out in answering them. If there are some questions you are unsure of, like how long you will be trekking or your exact route, just answer to the best of your knowledge and give yourself more time than less. The card will be checked at various police checkpoints along the trail and entering the reserve/conservation areas. The most useful thing they do is record your information as you pass certain checkpoints, leaving a definite trail of where you have been if something were to happen to you on the trail. In the past they used your passport info.
Again remember that if you are going to Annapurna to pick up your conservation area permit at the nearby counter, it costs 2,000 NRS. You can also get your ticket for the Langtang and Everest regions, but there is no need as they are available at the entrance to those regions for the same fee.