The "k" just denotes that it was made in Scotland, and otherwise it's the same as other Singer 99s, which were made from 1911 into the 1960'SThe Singer 99 was meant to be a smaller, more portable version of the classic Singer 66. It's made of cast iron, though, so it's still fairly heavy compared to most modern machines. You can print out a manual from Needlebar, I do not have one. The nice thing about vintage Singer sewing machines is that they almost always use bobbins and needles that are still in production today.
You can also still find parts for these machines fairly easily. Whether you want to use this machine or use it as a display item, it is very pleasing to the eye. The item "VINTAGE SINGER SEWING MACHINE 99k BZK. 12-12 GOOD CONDITION WORKING ORDER" is in sale since Tuesday, May 26, 2020.This item is in the category "Collectables\Sewing\Sewing Machines". The seller is "barre_3869" and is located in Frinton-on-Sea. This item can be shipped to United Kingdom, Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Australia, United States, Bahrain, Canada, Japan, New Zealand, China, Israel, Hong Kong, Norway, Indonesia, Malaysia, Mexico, Singapore, South Korea, Switzerland, Taiwan, Thailand, Bangladesh, Belize, Bolivia, Brunei darussalam, Dominica, Egypt, Guernsey, Gibraltar, Guadeloupe, Grenada, French guiana, Iceland, Jersey, Cambodia, Saint kitts and nevis, Liechtenstein, Macao, Monaco, Martinique, Nicaragua, Pakistan, Paraguay, Turks and caicos islands, Aruba, Saudi arabia, United arab emirates, Chile, Bahamas, Costa rica, Dominican republic, Guatemala, Honduras, Jamaica, Kuwait, Panama, Philippines, Qatar, El salvador, Trinidad and tobago, Uruguay, Antigua and barbuda, Bermuda, Barbados, Cayman islands, Jordan, Saint lucia, Sri lanka, Maldives, Oman, Reunion, South africa, Ukraine, Colombia, Montserrat, Russian federation.