Buying plants is synonymous with buying them in plastic pots. Indeed plastic revolutionised the horticulture trade by allowing plants to be grown in the pots themselves and distributed in bulk.
 In days gone by plants were grown in the soil and sold "bare root" i.e. dug up and the soil teased from the roots to make a smaller, lighter package. The plant can survive for a few days with some moisture provided for the roots e.g. wrapped in wet newspaper. The practice has largely disappeared but some nurseries still use this method.
 I bought the above from Shipton Bulbs who grow bulbs and wildflowers on a smallholding in Wales. Their plants are probably as close as you can get to actual wild plants without digging them up in the countryside which is quite rightly illegal.
 The photo shows bundles of 5 each of Field Scabious, Ox-eye Daisy, Greater Knapweed, Musk Mallow, Meadow Cranesbill and Betony. I'm going to plant them among the rough grasses in a corner of the allotment with the idea of creating a mini-meadow; all these species should do well in that setting.