From Jansson & Sylven (Histochemistry 78:121-4, 1983), the mean concentration of myoglobin in slow- and fast-twitch fibers from human vastus lateralis was 31 and 20 mg/g dry weight, respectively. Since most human muscle is mixed in terms of fiber type, you could estimate that the average muscle content is ~25 mg/g dry weight. If you want to convert to myoglobin content per wet weight of muscle multiply by 0.25 (i.e., the normal dry-to-wet weight ratio for muscle). You can estimate the total amount of muscle in the human body as 40% of body weight

A molecule of myoglobin can bind one molecule of oxygen (O2).

Sylven, Jansson, Book. Cardiovasc Rs 1984;18:443-6

No difference between untrained and trained skeletal muscle: c.1.2 micromol/g (dry weight). Myocardium lower (0.5 micromol/g dw). 

(Molecular weight c.17kDa)

http://cardiovascres.oxfordjournals.org/content/cardiovascres/18/7/443.full.pdf

Sarah Fallon, Ana Belcoe, Callan Shawcross, Alyssa May, Cristina Monteverde & Daniel McCann (2014): Elite Female Athletes' Ventilatory Compensation to Decreased Inspired O2 During the Wingate Test, Research Quarterly for

Exercise and Sport, DOI: 10.1080/02701367.2014.983448

We tried to get an idea of how much myoglobin bound O2 might contribute to O2 delivery during maximal exercise and came up with this conclusion. It is not directly related to your model, but I thing it is safe to assume that myoglobin O2 stores make a very minimal contribution even during maximal anaerobic exercise.

"Our experimental hypothesis was based on the assumption

that performing the Wingate test requires both

anaerobic and aerobic ATP production and maximally

stimulates both. This hypothesis also assumes that greater

deoxygenation of myoglobin (Mb) during hypoxia at

maximal exercise provides insignificant O2 for aerobic

metabolism.We believe this assumption is reasonable given

that Richardson, Noyszewski, Kendrick, Leigh, and Wagner

(1995) showed that only an 8% greater deoxygenation

of Mb (from about 52% to 60%) occurred when inspired

O2 was lowered to 12% during maximal leg exercise.

Because human muscle Mb concentrations are in the order

of 4.7 mg/g wet muscle (Reynafarje, 1962), an 8% greater

desaturation would result in providing only an additional

0.53 mL/kgmuscle of O2 for aerobic ATP production."

Reynafarje, B. (1962). Myoglobin content and enzymatic activity of muscle

and altitude adaptation. Journal of Applied Physiology, 17, 301–305.

Richardson, R. S., Noyszewski, E. A., Kendrick, K. F., Leigh, J. S., &

Wagner, P. D. (1995). Myoglobin O2 desaturation during exercise:

Evidence of limited O2 transport. Journal of Clinical Investigation, 96,

1916–1926.

We found (Bekedam et al 2009, J Appl Physiol 107, 1138-1143) 0.49 mM in type II and 0.7 mM in type I human skeletal muscle fibres. Myoglobin can supply oxygen for about 7 s at VO2max. Human myoglobin concetration varies considerably between different studies (for review see van Beek-Harmsen et al (2004) Histochem Cell Biol 121, 335-342).