You can adapt a scale for your need. E.g. if you need a scale for physical activity social support:
Rev Saude Publica. 2011 Apr;45(2):294-301.
Validity and reliability of a physical activity social support assessment scale.
Reis MS, Reis RS, Hallal PC.
If you need to measure social support in general check these out:
Effect of perceived social support and dispositional optimism on the depression of burn patients. He F, Zhou Q, Zhao Z, Zhang Y, Guan H. J Health Psychol. 2014 Aug 25.
Temperament traits, social support, and burnout symptoms in a sample of therapists. Rzeszutek M, Schier K. Psychotherapy (Chic). 2014 Dec;51(4):574-9.
Factors associated with perceived control and the relationship to quality of life in patients with heart failure. Heo S, Lennie TA, Pressler SJ, Dunbar SB, Chung ML, Moser DK. Eur J Cardiovasc Nurs. 2014 Jan 15.
The multidimensional scale of perceived social support: analyses of internal reliability, measurement invariance, and correlates across gender.Osman A, Lamis DA, Freedenthal S, Gutierrez PM, McNaughton-Cassill M. J Pers Assess. 2014;96(1):103-12.
Measuring the level of social support using latent class analysis. Santos LM, Amorim LD, Santos DN, Barreto ML. Soc Sci Res. 2015 Mar;50:139-46.
Effect of social support on depression of internet addicts and the mediating role of loneliness. He F, Zhou Q, Li J, Cao R, Guan H. Int J Ment Health Syst. 2014 Aug 16;8:34.
Compassion fatigue and burnout in Iranian nurses: The role of perceived social support. Ariapooran S. Iran J Nurs Midwifery Res. 2014 May;19(3):279-84.
Viswesvaran, C., Sanchez, J. I., & Fisher, J. (1999). The role of social support in the process of work stress: A meta-analysis. Journal of Vocational Behavior, 54(2), 314-334.
The 'peer support' subscale of the Health & Safety Executive's (HSE) stress management standards indicator might be worth a look. However, this subscale is only four items so, depending on your requirements, it may not be comprehensive enough for you if you need something in-depth.
If work gets difficult, my colleagues will help me
I get help and support I need from colleagues
I receive the respect at work I deserve from my colleagues
My colleagues are willing to listen to my work-related problems
The overall 35-item HSE scale is featured in quite a few papers, and has been well-validated. More info (e.g. questions, response format, etc) is available on www.hse.org.uk/stress.
Here are a couple of papers just to give you an idea...
Edwards, J. A., & Webster, S. (2012). Psychosocial risk assessment: Measurement invariance of the UK Health and Safety Executive's Management Standards Indicator Tool across public and private sector organizations. Work and Stress, 26(2), 130-142. doi: 10.1080/02678373.2012.688554
Edwards, J. A., Webster, S., Van Laar, D., & Easton, S. (2008). Psychometric analysis of the UK health and Safety Executive's Management Standards work-related stress Indicator Tool. Work and Stress, 22(2), 96-107. doi: 10.1080/02678370802166599
Houdmont, J., Kerr, R., & Randall, R. (2012). Organisational psychosocial hazard exposures in UK policing: Management standards indicator tool reference values. Policing, 35(1), 182-197.
Measure developed by Caplan et al., 1975 includes sub-scales that describe the support at employee perceives is available from his/her supervisor, coworkers, spouse, and family/friends.
Caplan, R. D., Cobb, S., French, J. R., Van Harrison, R., & Pinneau., S. R. (1980). Job demands and worker health. Ann Arbor: University of Michigan, Institute of Social Research.