The canonical bibliography of Royal proclamations is that of the Earl of Lindsey‘s commission, the two volumes of ‘Tudor and Stuart Proclamations 1485-1714’:
Volume 1: England and Wales. Google. Internet Archive. National Library of Scotland. Wellcome.
Volume 2: Ireland and Scotland. Google. Internet Archive. National Library of Scotland. Wellcome.
For proclamations after 1714, Lindsey bequeathed a less developed list, that includes orders in council and proclamations by other authorities, going up to 1910:
Handlist of proclamations issued by royal and other constitutional authorities, 1714-1910, George I to Edward VI. Google. Internet Archive. National Library of Scotland.
Finding the actual text of proclamations varies according to the period one is looking at, and one’s access to paywalled databases. For the Tudors and Stuarts, a full set has been compiled, in 5 volumes, all of which are available online, albeit paywalled or borrowable rather than downloadable.
Tudor Royal Proclamations, vol. 1: The early Tudors, 1485 – 1553: Borrowable from Internet Archive.
Tudor Royal Proclamations, vol. 2: The later Tudors, 1553 – 1587: Borrowable from Internet Archive.
Tudor Royal Proclamations, vol. 3: The later Tudors, 1588 – 1603: Borrowable from Internet Archive.
Stuart Royal Proclamations, vol. 1: James I, 1603 – 1625: Full text paywalled.
Stuart Royal Proclamations, vol. 2: Charles I, 1625 – 1646: Full text paywalled. Borrowable from Internet Archive.
After 1665, all Royal proclamations relating to Britain and Ireland are published in the London, Edinburgh or Dublin Gazettes. Those relating to colonial territories appear to be published in a more ad hoc fashion.
This site has a small collection of transcriptions of long eighteenth century proclamations.
Elsewhere, there is the collection ‘British Royal Proclamations relating to North America, 1603 – 1783’, available from Internet Archive and, in fully transcribed text, Project Gutenberg. And there is also a small collection of mobilization proclamations from 1914 at The Long Long Trail.