Hello Balaji.....

As per my memory, the following are the movies for which music compossed by K.V.Mahadevan. There are plenty, but these are some of them which I could collect from my rememberance:

For MGR:

1) Sabaash maapillai
2) Nallavan Vaazhvaan
3) Thaai Sollai Thattaathey
4) Thaayai kaaththa thanayan
5) Kudumba Thalaivan
6) Dharmam Thalai kaakkum
7) Neethikkuppin paasam
8) Vettaikaaran
9) Mugarasi
10) Kannithaai
11) Thanipiravi
12) Thaaikku thalaimagan
13) Vivasayee
14) Ther Thiruvizha
15) Kaadahl vaaganam
16) Nalla Neram
17) Adimai penn (Silver Jubilee)
18) Maattukkaara Velan (Silver Jubilee)
19) Pattikkaattu Ponnaiya
20) Annamitta Kai
21) En Annan

For Shivaji:

22) Padikkaatha Medhai
23) Kulamagal Raadhai
24) Kungumam
25) Navarathiri
26) Thiruvilaiyaadal (Silver Jubilee)
27) Selvam
28) Maha kavi Kaalidoss
29) Saraswathi Sabatham
30) Pesum Dheivam
31) Thiruvarut selvar
32) Thirumaal Perumai
33) Thillaana Mohanaambal
34) Vietnam Veedu
35) Ethiroli (Peculier 'kootani' of Shivaji, KB, KVM)
36) Kulamaa Gunamaa
37) Arunodhayam
38) Vasantha Maaligai (Silver Jubilee)
39) Engal Thanga Raja
40) Uththaman
41) Sathiyam
42) Vaani Rani

Others:

43) Aadhi Paraasakthi (Silver Jubvilee)
44) Panamaa Paasama (Silver Jubilee)
45) Saradhaa
46) Raththa Thilagam (shivaji)
47) Irulum Oliyum
48) Anaadhai Anandhan
49) Puthiya Vaazhkkai
50) Yeni Padigal
51) Ponnaana Vaazhvu

If anything come to my memory, I will continue.........