The schedule for upcoming testing dates at EXAMS is updated once a month. If you cannot find the test-date on the website of your test provider, it is  probably fully booked. 

TOEFL

April: 12 (AM + PM),  23 (PM)
May: 7 (PM), 31 (AM)
June: 21 (AM + PM)
July: 26 (AM)
August:  30 (AM)
September:  13 (AM)
October:  4 (AM + PM), 25 (AM)
November: 8 (AM),  22 (AM)
December: 6 (AM), 20 (AM)

IELTS

April: 11, 25
May: 9 , 15, 24
June: 6, 13, 20
July:  ---------
August: 16
September: 6, 20
October: 18
November: 1,  28
December: 13

Cambridge

April: 26
May: 10
June: 14

SELT for UKVI

April: 28
May: 5, 26
June: 7, 16
July: 29
August: 25
September: 19
October: 17
November: 14
December: 12

GRE

November: 26

SIELE

April: 22