In Finland the law dictates that you should use winter tyres between December 1st and March 1st but you would look ridiculous going up the M3 with tyres fitted with spikes. If that becomes fashionable the roadworks will increase by an order of magnitude.
The quick, dirty, and above all cheap way to obtain your first set of strings for the M3 is by topping up a standard set with a few singles. For example, you can use the 0.010, 0.013, 0.017, 0.036, and 0.046 from an ordinary roundwound set (leave out the D) and then buy a 0.022 and a 0.030 separately. You can use the following guages as a reference: 0.010 (high E), 0.013 (high C), 0.016 (high Ab), 0.022 (mid E), 0.30 (low C), 0.038 (low Ab), and 0.046 (low E). Remember that the high E and the low E are the top and bottom strings in an ordinary set so when you are deciding on the range of gauges, you are on familiar territory. If you prefer thinner, or thicker, strings you need to scale the guages up or down appropriately.
If you are serious about wanting to use strings that you cannot find in your local area, you might want to consider doing some internet shopping. I get my strings from Highly Strung in the UK, and dealing with them is fast and hassle-free. If you are based in the U.S. you are spoiled for choice, and you shouldn't have any problems finding an online retailer. I don't want to recommend any of them to you, though, since the two online retailers I contacted in the U.S. both ignored my email requests, and so I haven't been impressed with their customer service.