The following will give you a pseudo-random distribution of your attendees into 8 groups equal as possible (given that 300 = 8*37+4).
As the DocMan said, your lookup table needs to have a numeric Primary Key ranging from 1 to 8: GroupID, which will be the One side of the Attendees-Groups relationship.
We will create and populate a GroupID in your Attendees table, that will be the foreign key (Many side of the relationship).
I also assume that your Attendees table as a numeric PK ranging from 1 to 300 (AttendeesID). If this is not the case, re-post for a workaround.
1.
SELECT Attendees.*, ([AttendeesID] Mod 3)+1 AS GroupID
FROM Attendees;
This select query makes the distribution, creating and populating the GroupID field. Save it.
2.
MAKE A COPY of your attendees table (copy and paste it with a different name in the tables window)
3.
Transform the above query into a Make-Table one: open it in edit mode, then in the queries Menu choose Make-Table. Give the name of your Attendees table, you will be prompted for a confirmation.
4.
BE SURE that you made that copy.
5.
Confirm
The result is not actually a random distribution since it is made according to a regular pattern, and your attendees in your Attendees table may also have be entered according to some logic. So this could not be used as panel for statistic purposes for example.
Nevertheless, it should be a satisfying approach to a random distribution for your specific purpose.
Alex