Best Link is where I put links provided by professional nurserymen, plant collectors and hybridists who were willing to write a short paragraph for inclusion here.
Below are links provided by; Peter D. A. Boyd (collector of Scots roses), Harold Greer of Greer Gardens (mail order rare and unusual plants), As I add them below I'll list them here.
Peter D. A. Boyd is a collector and plant writer on Scots Roses. You are welcome to put a link to my website on your site. I have just put another article on the site that was translated into French for publication in France. There are links to both the French and English versions. All my articles on Scots Roses are listed on http://www.peterboyd.com/scotsroses.htm with links to the web versions. Of these 'A Personal Crusade in Search of Scots Roses' at http://www.peterboyd.com/rosapimp6.htm is probably the most useful for you. The true Scots Roses are all very hardy and most are disease-resistant. However, the yellow ones which are probably all hybrids with Rosa foetida (different single and double forms of Rosa x harisonii including 'Williams Double Yellow) can be affected by black-spot - but they are still worth growing. Peter Beales has one of the best selections of Scots Roses available for sale in Britain at http://www.classicroses.co.uk/roses/family/pimpinellifolias even though his 'Mary Queen of Scots' is not the double purple form with pale backs to the petals. I direct you to this list because it includes pictures and is representative of what is available in commerce in Britain. However, the selection is still limited. Some other cultivars are available in other countries but sometimes include the same cultivars as in Britain under different names.
David Austin at http://www.davidaustinroses.com (look under 'Wild Roses and their hybrids') and Acton Beauchamp Roses at http://www.actonbeaurose.co.uk (look under 'Scots Briars') are two other nurseries with a selection of the Scots Roses available in Britain.
A search for Rosa spinosissima in the RHS Plant Finder at http://www.rhs.org.uk/rhsplantfinder/plantfinder.asp will provide names of other nurseries in Britain that stock Scots Roses ( see http://www.rhs.org.uk/rhsplantfinder/plantfinder2.asp?crit=rosa%20and%20spinosissima&Genus=Rosa ).
The very small number of cultivars stocked by nurseries in Britain (often mis-named) is in contrast to the hundreds of 'varieties' that were available in the past or even to the number in my personal collection. I hope that I will gradually be able to introduce other cultivars from my collection into commerce but collections such as the Europa-Rosarium at Sangerhausen have first call on suckers when my plants are large enough to provide spare material.
'Harison's Yellow' is, of course, one of the Rosa x harisonii group. There are several different double yellow forms of Rosa x harisonii (as well as single forms) and I am not sure that all the plants sold as 'Harison's Yellow' are the same cultivar. Plants with names such as 'Old Yellow Scotch' are similar but some have a more pleasant scent than others. Personally, I prefer the flower form of 'Harison's Yellow' and 'Old Yellow Scotch' types to 'Williams Double Yellow' which gives a good show but in which the individual flowers are rather untidy.
I hope that this is helpful. Best wishes, Peter
Peter D. A. Boyd
Harold Greer provided the following on November 14, 2006.
Greer Gardens has been established for about 50 years selling rare and unusual plants. Originally the nursery sold rhododendrons to the local community, but in 1968 the first plant list was sent out to a handful of customers. From that beginning we issued a 164 catalog selling about 4500 different kinds of plants. We continue to specialize in rhododendrons, but have expanded to sell one of the largest collections of Japanese Maples, plus, conifers, camellias, magnolias, perennials and 1000 or so unusual trees, shrubs and vines. We now sell mail order all over the US and many other countries. We operate from 14 acres of land in Eugene, Oregon. Our website is www.greergardens.com
http://www.rosefile.com/RosePages/ColdClimate.html a list of roses hardy in zone 3